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The Enzymes – Short Questions Answers

Biology XI Notes

Chapter # 03
Short Questions Answers
Section II – Unity Of Life

THE ENZYMES

Q.1: What are enzymes and what are the characters of enzymes?

Ans: ENZYMES:
Enzymes are the organic proteinaceous substances which catalyze chemical reactions in the living organisms. These are considered as bio-catalysts. They increase the rate of chemical reaction but are not consumed in the process:

The term enzyme was used by a scientist, Friedrich Wilhelm Kuhn in 1878.

Characteristics Of Enzymes:

Enzymes are made up of proteins. They are big molecules with higher molecular weight.
They can react with both acidic and alkaline substances due to the presence of proteins.
In a biochemical reaction, only a small amount of enzyme is required as compared to the substrate.
Enzymes are not consumed during the reaction. They remain unaffected and can be used again and again.
The enzymes catalyze only specific reactions, that is, each individual enzyme is restricted in its catalytic activity to one particular reaction or one group of related chemical reactions.
Their activities can be accelerated by certain ions or salts, called activators, such as Ni, Mn, Mg, Cl, etc.
They do not initiate the reaction, but only increase its rate by lowering the energy of activation.
Some enzymes contain a non-proteinaceous part, called Prosthetic group.
When many different enzymes catalyze the same chemical reaction, they are known as isoenzymes.
The enzymes have a specific active centre which is attached to the substrate. If this active centre is bonded with another substrate, then the enzyme loses its activity.
Enzymes are sensitive to change in temperature and pH. Heat, alcohol and concentrated solution of inorganic acids stop the activity of enzymes.

Q.2: What are the types of enzymes?
OR
Describe the structure and composition of Enzymes?

Ans: STRUCTURE AND COMPOSITION OF ENZYMES: (TYPES OF ENZYMES)
The enzymes are basically proteinaceous in nature. They have relatively high molecular weight of 40,000 and Catalase has a molecular weight of 250,000.

Certain enzymes consist only of protein; they are called simple protein enzymes. Many enzymes have an attached non-protein group; they are known as conjugated protein enzymes or holoenzymes. It was proposed by Euler in 1932. The holoenzyme consists of two parts:

The protein part, called apoenzyme.
The non-protein part, called prosthetic group.

On the basis of prosthetic group, the holoenzymes are of two types:

With inorganic ions: When the prosthetic group is an inorganic ion, it is called co-factor, such as Mg, Ca, K, Mn, etc. e.g. Phosphatase, carboxylase, Peptidase, Amidase, etc.
With organic compound: When the prosthetic group is an organic compound, this organic compound is called co-enzyme. It has only 1% part of whole enzyme.
e.g.

NAD (Nicotine amide adenine dinucleotide)
NADP (Nicotine amide adenine dinucleotide phosphate)
ATP (Adenosine triphosphate)

Q.3: Describe the function or mode of action of enzymes?

Ans: MODE OF ACTION:
The action of enzyme depends upon the structure of enzyme. It has three-dimensional structure. It has an active site, which is of a particular size and shape. This active site is attached with substrate.

Fischer (1898) proposed a theory about the action of enzyme, called key-lock theory. This theory was improved by Paul Filder and D.D. Woods. According to the theory, each enzyme can react with a specific substrate in the manner of a lock and key, just like a lock can be unlocked by a particular key.

The site of enzyme which is active and attached with substrate is called active site. This site helps in the catalytic action. Sometimes other molecules are connected with active site, but there is no bond formation and no chemical reaction.

Koshland in 1959 proposed another theory about the action of enzymes, called Induce Fit Model Theory. According to this theory, when enzyme combines with a substrate, some changes occur in the structure of enzyme, due to this change the enzyme performs its catalytic function in more effective manner.

Q.4: Describe the different factors of enzymes?

Ans: FACTORS AFFECTING ENZYME ACTIVITIES:
Following factors affect the enzyme activity.

Temperature
Substrate concentration
pH
Co-enzyme, activators, and inhibitors
Water
Radiation

Temperature:
Enzymes are sensitive to heat. They lose their activity at high temperature. The enzymes are denatured by heat, i.e., they are destroyed. The optimum temperature for most of the enzymes is 30°C to 37°C. At freezing point, they become inactive but are not destroyed; at 100°C, the enzymes are completely destroyed.

Substrate Concentration:
With the increase of substrate concentration, the rate of reaction is also increased. The enzyme molecule is much larger than its substrate. When concentration of substrate is low, the active sites on the enzyme molecule may not be occupied; thus, the enzyme does not work. When enzyme is saturated with substrate concentration, then the rate of reaction becomes independent of concentration, and further increase in substrate has no effect.

pH:
Each enzyme has an optimum pH at which the enzyme shows maximum activity. Change in pH can cause loss of its activity. It can be destroyed. When pH scale is shifted to the alkaline or acidic side, its activity is dropped. The optimum pH of pepsin is 1.6 (acidic), while pH of trypsin is 8.2 (alkaline).

Co-Enzymes, Activators, And Inhibitors:
Other groups, such as co-enzymes and co-factors, increase or decrease the enzyme action. These groups are of three types:

Co-Enzymes:
The organic molecule of enzyme is called co-enzyme. Its presence increases the activity of certain enzymes. Without these co-enzymes, their activity is stopped. e.g., COA, NAD, FAD, etc.
Activators:
Activators are the inorganic substances which increase the activity of enzyme; for example, Phosphatase enzyme has Mg⁺² as an activator, and Zn⁺² is the activator of enzyme carbonic anhydrase.
Inhibitors:
Inhibitors are the substances which decrease the activity of enzyme. These inhibitors either attach directly with enzyme or its activator, then the activity of enzyme is stopped. The inhibitors are of two types:
- Competitive inhibitors
- Non-competitive inhibitors
Competitive inhibitors:
These inhibitors resemble the normal substrate, these are attached with the active site of enzyme, so take part to reduce the function of enzyme. If the reaction is reversible, it can be controlled by increasing the concentration of substrate; in this way the substrate gets site of enzyme for attachment and reaction is proceeded.
Non-Competitive Inhibitors:
When certain substances are attached to a part of enzyme, away from active site, its activity is affected; such inhibitors are called non-competitive inhibitors. By the attachment of these substances, the enzyme becomes less active. The binding site other than active site is called Allosteric site.
Water:
Water also plays an important role to affect the activity of enzymes. In germinating seeds, water enters the body and helps to produce enzymes. The enzymes become active during germination.
Radiation:
Ultraviolet rays, n-rays, γ-rays, and x-rays destroy the activity of enzymes.

Q.5: Write a note on Feedback inhibition?

Ans: FEEDBACK INHIBITION:
When product is formed in a chemical reaction, it binds with its enzyme; it is called feedback inhibition. It regulates the activity of enzymes. When the product is in more amount, it is attached competitively with enzyme's active site. The product is used, then inhibition is reduced, as a result of which more product is formed.

In some enzymatic reactions, the end product binds non-competitively at allosteric site on the first enzyme of the reaction. This binding stops the reaction and no more product is formed.

Biology XI Notes - The Biology - Short Questions Answers

Chapter # 01 - Biology - XI

Short Questions Answers Section I - Introduction

Q.1: What is Biology?

Ans:
Biology is one of the natural sciences, which deals with the study of living organisms. It is known as the study of life. The word "biology" is derived from Greek words "Bios" meaning life and "Logos" meaning study or knowledge.

Formerly, living organisms were classified into two kingdoms:

Plant Kingdom:
In this kingdom, plants were included. The study of plants is called Botany.
Animal Kingdom:
In this kingdom, animals were included. The study of animals is known as Zoology.

Q.2: Write a note on Five Kingdoms Classification?

Ans:
According to modern research, the old system of classification has been discarded. Now, all living organisms are classified into five kingdoms. This system was proposed by Robert Whittaker in 1969 and was later modified by two American biologists, L. Margulis and K. Schwartz.

Kingdom - Monera:
This kingdom includes all the prokaryotes. These are simple living organisms which do not contain a complete nucleus in their cells, e.g., Blue-green algae, Bacteria.
Kingdom - Protoctista (Protista):
This kingdom includes three kinds of living organisms:
- Animal-like:
  Unicellular protozoan organisms like Amoeba, Euglena.
- Plant-like:
  Algae - simple water-living organisms that contain chlorophyll.
- Fungi-like:
  Slime mold, water mold.
Kingdom - Fungi:
This kingdom includes multi-cellular, non-green thallophytes that have a very simple body called mycelium. They have a cell wall, and their body may be coenocytic (multinucleate). Due to the absence of chlorophyll, they cannot manufacture their own food, so they are either parasites or saprophytes, e.g., Agaricus (Mushroom), Yeast.
Kingdom - Plantae:
This kingdom includes multi-cellular, eukaryotic organisms that have a complete nucleus in their cells. They usually contain chlorophyll and can manufacture their own food, e.g., Mustard, Sunflower, Apple.
Kingdom - Animalia:
This kingdom includes multi-cellular eukaryotic organisms with a complete nucleus in their cells. They do not contain chlorophyll and have no cell wall, e.g., Hydra, Earthworm, insects, Frog, Birds, Fishes, Man.

Q.3: What are the major branches or fields of Specialization of biology?

Ans:
Some major branches or fields of specialization in biology are as follows:

Molecular Biology:
It is a modern branch of biology focusing on the structure and function of molecules that support biological processes in living organisms, such as nucleic acids, gene structure, proteins, and protein synthesis. It is the foundation of genetic engineering.
Microbiology:
It deals with the study of micro-organisms, such as viruses, bacteria, and protozoans.
Environment Biology:
This branch studies the environment and its impact on organisms.
Marine Biology:
It focuses on organisms found in seawater or ocean water and examines their physical and chemical environmental characteristics.
Fresh Water Biology:
This branch studies life found in freshwater environments like rivers, lakes, ponds, and streams, including the physical and chemical characteristics affecting life.
Parasitology:
This branch examines parasitic organisms, their lifecycle, disease transmission, and interactions with hosts.
Human Biology:
It covers all aspects of human life, including anatomy, physiology, health, inheritance, and evolution.
Social Biology:
It studies the social activities of animals within populations, especially humans, and considers behavior that may be inherited from parents or developed due to environmental factors.
Biotechnology:
It is a very modern and recent branch of biology. It deals with the study of (i) the use of data and techniques of engineering; and (ii) technology for studying and solving problems related to living organisms, especially in human beings.

Q.4: What are the different levels of biological organization?

Ans:
All living organisms have well-organized and highly complex bodies. This biological organization is not simple and is composed of different levels, starting from the basic level of sub-atomic and atomic particles up to the high level of individual whole organisms.

The levels of biological organization are as follows:

Atomic and sub-atomic level
Molecular level
Cell and organelles level
Tissue level
Organ and organ system level
Individual whole organism level
Broader levels of organization:
- Species population
- Community
- Ecosystem
- Biosphere

Q.5: Define the following terms:

Symbiosis
Commensalism
Mutualism
Parasitism

Ans:
Defining the following:

Symbiosis:
When two living organisms live together in a way that is beneficial to both, it is called symbiosis.
Commensalism:
The association between two organisms in which one benefits, while the other remains unaffected or gains no harm or benefit, is called commensalism. For example, saprophytic bacteria in the animal gut.
Mutualism:
This is an association between two or more organisms in which both benefit from the relationship. When separated, both species can survive independently.
Parasitism:
When two living organisms live together in such a way that one organism benefits and the other is harmed, it is called parasitism. For example, Plasmodium causes malaria in humans.

Q.6: What is the biological method? Explain hypothesis.

Biological Method:
The method used to solve problems in biology through observation, data collection, and experimentation is called the biological method.

Steps of the biological method are as follows:

Observation:
It is the identification of a biological problem. Through deep observation, the problem can be understood properly.
Data Collection:
Deep observation helps to gather all facts and information about the work, which has been reported by others. This process is called data collection.
Hypothesis:
Based on these facts and information, a tentative statement is prepared by the scientist, known as a hypothesis.
Reasoning:
The hypothesis can guide further observations and experiments. Reasoning can be of two types:
- Inductive Reasoning:
  Isolated facts are used to form a general idea to explain a phenomenon.
  Example: In 1665, Robert Hooke observed a piece of cork under a microscope and identified small chambers, which he called cells. This work contributed to further cell research, leading to the cell theory by M.J. Schleiden and T. Schwann.
- Deductive Reasoning:
  This involves general assumptions and experiments to reach a conclusion.
Experimentation:
In the biological method, further experiments are necessary to achieve accurate results.
Conclusion:
On the basis of experiments, observations, and new data collection, conclusions are drawn.
Theory:
A theory is presented to the world based on conclusions. If the hypothesis is true, the theory is accepted; otherwise, it is rejected.
Law:
When a theory is accepted and proven true, it is considered a general principle, i.e., a law.

Q.7: Write a note on the importance of biology?
OR
Application of biology for the welfare of mankind?

Ans:
Application of Biology for the Welfare of Mankind:
Biology is a very important field of science with great significance for the welfare of mankind. Its applications include:

Helping to improve the standard of life.
Promoting better health.
Assisting in the protection and conservation of the environment.
Applying modern technology in agriculture to improve the quality and quantity of crops, solving food and other essential issues.
Utilizing modern technology in medical sciences.

Some applications of biology in medical sciences are as follows:

Immunization:
Immunization, or resistance against diseases, is achieved through vaccination worldwide. This technique has helped control diseases like polio, smallpox, and hepatitis, significantly reducing infection and infant mortality rates. Edward Jenner first introduced vaccination in 1795 to protect against dangerous diseases like polio, hepatitis, and smallpox.
Antibiotics:
Antibiotics are substances used to inhibit the growth of microorganisms. The first antibiotic, Penicillin, was isolated from the fungus Penicillium notatum. This work, done by Fleming, Flory, and Chain, earned them the Nobel Prize. Antibiotics are widely used to control diseases such as TB, cholera, leprosy, and anthrax.
Chemotherapy:
Biology constantly aims to develop new medicines for disease treatment. Recently, harmful diseases like AIDS and cancer are treated with certain chemicals in a process called chemotherapy.
Radiotherapy:
The use of radioactive rays (X-rays) is widely used in treating diseases. This technique is called radiotherapy, which is also useful for diagnosing diseases. Radiotherapy is primarily used to treat cancer, but it is expensive and painful.
Food Shortage Due to Population Increase:
Due to the increase in population, there is always a shortage of food and other necessities. Modern technology in agriculture and related fields can help increase food production.

Q.8: What is Hydroponics?

Ans:
Hydroponics:
It is a soil-less or water culture technique in which terrestrial plants are grown in an aerated solution. This technique allows vegetables and other plants to grow, helping meet the food needs of a particular area. Tomato crops and other vegetables are cultivated in greenhouses using this technique, yielding satisfactory production.

Advantages of Hydroponics:
Using this technique, crops can be protected from soil diseases and weeds. In dry regions, some crops can be grown successfully. For example, tomatoes and other crops are cultivated in greenhouses for production.

Q.9: What is Cloning?

Ans:
Cloning:
Cloning is a modern technique in biological science that produces duplicate copies of genetic material. It is a method of asexual reproduction, with all cloned members being genetically identical. Examples include regeneration, asexual reproduction in animals and plants, human twins, and cancer tumors.

In 1996, scientists in Scotland successfully cloned a sheep named "Dolly." This technique is successfully applied in lower mammals.

Procedure of Cloning:
In cloning, the nucleus of an egg is removed, and a nucleus from a fully developed individual is introduced into the egg.

The modified egg is then implanted into a female's womb for complete development. The resulting individual is very similar to the one whose nucleus was used.

Importance of Cloning:

By cloning, different kinds of human cells can be prepared, such as liver cells, skin cells, and blood cells. This may enable the development of human body organs, allowing defective organs to be replaced by cloned ones.
This technique can improve quality in agriculture and medical sciences.
Growth hormones, insulin, and other substances can be produced through cloning.
Cloning can reduce the area needed for cultivation.
It can also help in determining essential minerals and understanding plant structures.

Q.10: Write a note on Protection and Conservation of Environment?

Ans:
Human beings and other organisms live in a particular environment that provides nourishment and basic needs. This environment faces damage in various ways.

Pollution:
Pollution harms our environment and exists in multiple forms, such as air, water, and land pollution. Acid rain, greenhouse effects, and waste matter with toxic substances contribute to pollution, directly affecting the lives of organisms.
To protect the environment, practical methods to reduce or minimize pollution are essential. A healthy environment is necessary for all living organisms.
Deforestation & Industrialization:
Activities like deforestation, industrialization, and other human interventions disturb the natural biological systems in the environment.
Conserving forests helps reduce soil erosion and flooding. By protecting various plant and animal species, a stable and balanced ecosystem can be maintained.

Nuclear Radiations - Question Answers - Physics XII

Q.1: Explain how you would test whether the radiation from a radioactive source is α, β or Gamma radiation?

Ans: When radiations are allowed to pass through a magnetic field, the α and β particles are deflected while γ-rays pass through undeflected. This technique helps to identify the radiation.

Q.2: A particle which produces more ionization is less penetrating. Why?
Ans: When a particle ionizes an atom, it loses a part of its energy. Since the greater the ionizing power, the greater is the loss of energy; and hence, the smaller is its penetrating power.

Q.3: It is said that α or β particles carry an atom without colliding with its electrons. How can each do so?
Ans: An α-particle is positively charged and a β particle is negatively charged. So an α particle ionizes an atom by attraction while a β particle ionizes an atom by repulsion.

Q.4: In how many ways can Gamma rays produce ionization of the atom?
Ans: Gamma rays only ionize an atom by collision. Being a high-energy photon, it can produce ionization in three ways:
i. it may lose all its energy in a single collision with the electron of an atom (photoelectric effect);
ii. it may lose only a part of its energy in a collision (Compton effect);
iii. it may be stopped by a heavy nucleus giving rise to electron-position pair (materialization of energy).

Q.5: In what way does a neutron produce ionization of an atom?
Ans: A neutron collides with a substance containing a large number of hydrogen atoms and knocks out a proton. In this way, it causes ionization.

Q.6: Name different electromagnetic radiations that are capable of producing ionization of atoms. By what process do they ionize?
Ans:
i. Ultraviolet rays
ii. X-rays
iii. Gamma rays

The rays interact with matter inelastically. They remove electrons from the atoms of the target material.

Q.7: Why is lead a better shield against α, β, and gamma radiations than an equal thickness of a water column?
Ans: α and β particles do not travel far enough in water due to intense ionization they produce. Reduction of gamma rays' beam intensity is a measure of its range, which is considerably more. However, materials having large numbers of electrons per unit volume are more effective absorbers of gamma radiations. When gamma rays are incident on lead, then, because of the photoelectric effect, they lose their energy in a single encounter and travel only a small distance. But as water has fewer electrons than lead, so gamma rays lose less energy and penetrate through a larger distance in water. Hence, lead is a better shield against gamma rays than water.

Q.8: Lead is heavier and denser than water. Yet water is more effective as a shield against neutrons?
Ans: To be stopped or slowed down, a neutron must undergo a direct collision (elastic) with a nucleus or some other particle that has a mass comparable to that of the neutron. Water contains hydrogen. Thus nuclear protons of hydrogen atoms, after collision, move; while the neutron is slowed down. But when neutrons collide with the nucleus of lead, it bounces neutrons back almost with the same speed. Hence, water is a better shield against neutrons than lead.

Q.9: In an X-ray photograph, bones show up very clearly, but the fleshy part shows very faintly. Why?
Ans: X-rays can be stopped by bones, but they can penetrate flesh.

Q.10: In a cloud chamber photograph, the path of an α particle is a thick and continuous line, whereas that of a β particle is a thin and broken line. Why?
Ans: An α-particle is highly ionizing than a β-particle.

Q.11: Why do gamma rays not give line tracks in the cloud chamber photograph?
Ans: Gamma rays do not produce ionization directly. They interact with atoms to eject electrons. These electrons, like β particles, produce irregular cloud tracks of their own, which branch out from the direction of gamma rays.

Q.12: A neutron can produce little ionization. Is there any sure chance of getting a cloud chamber track for it to count in the Geiger counter?
Ans: Neutrons are unable to ionize a gas. However, ionization is only produced when a neutron strikes directly a nucleus or a hydrogenous material, e.g., body tissues. The knocked-out proton produces ionization in the Geiger counter.

Q.13: A cloud chamber track of an α particle sometimes shows an abrupt bend accompanied by a small branched track. What could possibly be the cause of this forked track?
Ans: When an α-particle strikes a nucleus, the recoiling nucleus leaves a track. This is the cause of a forked track.

Q.14: Why is the recommended maximum dose for radiation a bit higher for women beyond the childbearing age than for young women?
Ans: It has been found that ovary and grown follicular cells are most sensitive cells for radiation. But primordial follicles and oocytes are more radiation repellent, and they grow even after irradiation. Also, the fertility of ovary is much affected when the whole body is irradiated by a specific dose of radiation (e.g., 200 RAD) than when ovary alone is irradiated by the same dose.

Q.15: It is possible for a man to burn his hand with x- or γ-rays so seriously that he must have it amputated and yet may suffer no other consequence. However, a whole-body x- or γ-ray overexposure so slight as to cause no detectable damage might cause birth deformity in one of its subsequent children. Explain. Why?
Ans: The damage to body cells, caused by very high doses of radiation, can be as serious as to stop them from working and multiplying. Widespread damage of cells may kill people. Delayed effects, such as cancer, leukemia, deformity, and mental retardation in children and grandchildren, may take place due to genetic syndromes.

Q.16: Which of α, β, and γ rays would you advise for the treatment of (i) skin cancer (ii) the cancer of flesh just under the skin (iii) a cancerous tumor deep inside the body?
Ans:
i. For the treatment of skin cancer, we use α-particles, as their penetration is small.
ii. For the treatment of cancer of flesh just under the skin, β-particles should be used because of their medium penetration power.
iii. For the treatment of deep infection in the body, γ rays should be used, as they are highly penetrating.

Q.17: Two radioisotopes of an element are available: one of long half-life and the other of short half-life. Which isotope is advisable for the treatment of a patient and why?
Ans: For the treatment, radioisotopes of short half-life should be used so that any material remaining in the body quickly decays away.

Q.18: Why are many artificially prepared radioisotopes of elements rare in nature?
Ans: Many artificially prepared radioisotopes of elements are rare in nature because of their extremely small half-life.

Q.19: Can radiocarbon dating be used to measure the age of stone walls of ancient civilizations?
Ans: No, radiocarbon dating cannot be used to measure the age of stone walls. "Carbon-14 clock" can be used for organic archaeological samples (i.e., matter that was once living). However, a "uranium clock" can be used for this purpose.

Q.20: How can a radioisotope be used to determine the effectiveness of a fertilizer?
Ans: When P-32 is given to a plant mixed with water, the amount of the chemical absorbed by various parts of the plant is checked by a G.M. counter. This technique helps to find the exact amount of the fertilizer required.

THE ATOMIC NUCLEUS

Chapter – 19

Q.1: How many neutrons and protons do the following nuclei contain?

Nuclide	Protons	Neutrons
$^{27}_{13}Al$	13	$27 - 13 = 14$
$^{40}_{18}Ar$	18	$40 - 18 = 22$
$^{138}_{56}Ba$	56	$138 - 56 = 82$
$^{207}_{82}Pb$	82	$207 - 82 = 125$
$^{28}_{14}Si$	14	$28 - 14 = 14$
$^{238}_{92}U$	92	$238 - 92 = 146$

Q.2: Do $\alpha$ , $\beta$ , and gamma rays come from the same element? Why do we find all three in many radioactive samples?
Ans: A radioactive element either emits $\alpha$ -particles or $\beta$ -particles, but never both. Gamma radiations generally accompany $\beta$ -emission and, in some cases, with $\alpha$ -emission.

A radioactive element (or sample) is a mixture of various nuclides of different relative abundances and with different modes of disintegration. Hence, we can find all the three types of radiations in a radioactive sample at the same time. For example, R-226 is an $\alpha$ -emitter, but Ra-25 is a $\beta$ -emitter.

Q.3: It is more difficult to start fusion reaction than fission. Why?
Ans: Fission is caused by captured neutrons by heavy nuclei. Neutrons, being electrically neutral, are highly penetrating particles for nuclei. But in fusion of two light nuclei, the positively charged nuclei are repelled by the repulsive forces. So work has to be done against the repulsive forces of the two nuclei.

Q.4: Is it possible that fusion of two small nuclei may occur without collision at extremely high energy?
Ans: No. Two nuclei must collide with sufficient kinetic energy to penetrate their mutual “Coulomb Barrier” and come within the range of the nuclear forces.

Q.5: Explain how a nuclear reactor produces heat as a result of fission?
Ans: In fission, the difference of binding energies of reactants and products is converted into energy. The difference of mass (0.22u) appears as energy (200 MeV). If fission takes place in a bulk solid, most of the disintegration energy appears as an increase in the internal energy of the solid, which shows a corresponding rise in temperature. This thermal energy is carried away to the heat exchanger by circulating the coolant through the reactor.

Q.6: What are the benefits and risks of nuclear reactors? Which reactor is relatively better from the point of safety?
Ans: Nuclear reactors are used to produce (i) electricity, (ii) nuclear fuels, and (iii) radioisotopes. These are peaceful uses of nuclear energy; the reactor fuel is clean burning and relatively easy to transport.

The risks of reactors include the possibility of safety hazards for the workers, environmental damage near the plant, the problem of storing highly radioactive wastes, and a limited supply of raw materials. Nuclear reactors have built-in safety devices. The accidental problems, such as leakage of radioactive substances, could occur if safety features malfunctioned. Pressurized water reactors, using water as a moderator and coolant, are safer with shut-off control rods and liquid "poison."

Q.7: Both fission and fusion apparently produce energy. How can you reconcile this with the law of conservation of energy?
Ans: In fission of U-235 with thermal neutrons, the loss of mass (0.2153 u) is converted into energy, producing about 200 MeV per fission.

In fusion, four protons may be combined to produce one helium nucleus and two positrons. Here, the losses of mass (0.027 u) are converted into energy, producing about 26 MeV. Thus, in both cases, the total "mass-energy" remains conserved.

Q.8: When a photon disappears in producing an electron and a positron, is the energy of a photon equivalent to that of the particles produced? Explain.
Ans: No, the energy of the photon is always greater than the rest mass energy of elements (electron and positron pair, 1.02 MeV). The surplus energy is taken by the two particles as their kinetic energy.

Q.9: When a neutron decays into a proton and an electron, there would be a loss of mass. What would be the energies of the products and their relative directions of motion?
Ans: Neutron is not a stable particle outside nuclei. It decays into a proton, an electron, and an antineutrino. The half-life of the free neutron is 10.8 min.

$^0n^1 \rightarrow ^1p^1 + e^0 + \nu$

Mass of neutron = 1.008649 u = 939.58 MeV
Mass of proton = 1.0072766 u = 938.23 MeV
Mass of electron = 0.000549 u = 0.511 MeV
Mass of proton + electron = 1.0078256 u
Loss of mass = 1.0086469 - 1.0078256 = 0.0008393 u = 0.78 x 18 MeV

These would be the energies of the products. Due to their kinetic energies, the two particles will move apart (and not be attracted).

Q.10: Why do most moderators, used in nuclear reactors, are light atoms like $H^1, H^2,$ $C^{12}$ slow down the neutrons, and hence they are slowed?
Ans: Fast moving neutrons can be stopped when they make elastic collisions with stationary particles of the same mass. Since the mass of protons, deuterons, or graphite nuclei is comparable to the mass of neutrons, hence they are slowed.

Q.11: Can a conventional fission reactor ever explode like a bomb does? Why?
Ans: In a nuclear reactor, a fission explosion is not possible because the amount of fuel (e.g., U-235 or Pu-239) is of sub-critical mass and it can shut off control rods in emergencies. Also, liquid "poison" can be inserted directly into the moderator if other safety devices fail.

Q.12: In LMFBR, would you expect the radioactivity of the sodium coolant to include the life time of the reactor?
Ans: Yes, because sodium can capture neutrons.

$^{11}\text{Na}^{12} + ^0\text{n}^1 \rightarrow ^{11}\text{Na}^{24} + \gamma$

Here, Na-24 is radioactive (beta and gamma emitter) with a half-life of 15.0 h.

Q.13: Consider a sample of 1000 radioactive nuclei with a half-life T. Approximately, how many will be left after a time 3T?
Ans: The number of nuclei decayed in one half-life (T = T) are 500. Also, the number of nuclei that decay in three periods of half-life are $1000/2^3$ . Hence, the number of nuclei left undecided is 125.

Q.14: What is the condition for “critical mass?”
Ans: If the mass of fissile material is such that the multiplication factor k > 1, then fission is said to occur in a critical mass. The multiplication factor is the ratio of the number of neutrons in any particular generation to the number of neutrons in the preceding generation. In a reactor, it is slightly above 1; but in a fission bomb, it is about 2.5.

Q.15: Why is heavy water more efficient as a moderator than ordinary water?
Ans: Heavy water (D₂O) has a much lower probability of capturing neutrons, but it can slow down neutrons. In fact, heavy water is 1600 times more efficient as a moderator than ordinary water (H₂O).

Q.16: In LMFBR, why is water not used as a coolant instead of liquid metal?
Ans: If water is used as a coolant in LMFBR, it slows down the neutrons through collisions and hinders the process of breeding (which requires less neutrons to convert U-238 into Pu-239). Also, the probability of capturing neutrons for water is high. Moreover, high pressure is needed to stop vaporization of water, and the core is heated up.

Sodium is a solid at room temperature but becomes liquid at 98°C. Hence, there is no need to pressurize the reactor to keep the sodium from vaporizing. Sodium is highly valued for thermal conductivity and heat transfer coefficient.

Q.17: Why are breeder reactors a necessity?
Ans: The world’s deposit of fossil fuels may not last more than 500 years, and nuclear fuels may not last for more than 5000 years. So, reactors that generate more nuclear fuels than they consume—breeder reactors—are a necessity.

THE ATOMIC SPECTRA

Q.1: The Bohr’s theory of hydrogen atom is based upon several assumptions. Do any of these assumptions contradict classical physics?
Ans: The assumption in Bohr’s theory that an electron moving around the nucleus in a certain orbit does not radiate energy is contrary to classical electrodynamics.

Q.2: Why does the hydrogen gas produced in the laboratory not glow and emit radiations?
Ans: A spectrum is given by the light emitted from an incandescent gas or vapour e.g., electric discharge through a gas or hydrogen-filled discharge tube.

Q.3: Why are the energy levels of the hydrogen atom less than zero?
Ans: The energy levels of the hydrogen atom are negative. This shows that the electron is bound (not free). Thus, one must do work (or expend energy) to remove it from the atom.

Q.4: If the hydrogen gas is bombarded by electrons of energy 13.6 eV, would you expect to observe all the lines of the hydrogen spectrum?
Ans: If a hydrogen atom is bombarded by electrons of energy 13.6 eV, it gets ionized; because 13.6 eV is the ground state energy, which is equivalent to the ionization energy. As such, no spectral lines of hydrogen will be observed.

Q.5: Hydrogen gas at room temperature absorbs light of wavelengths equal to the lines in the Lyman series but not those in the Balmer series. Explain?
Ans: Hydrogen gas at room temperature contains electrons in the ground state (p=1). If the energy supplied to the electron is such that the electron is lifted from its ground state to one of the higher allowed orbits, the atom will be excited, and it will absorb energy equal to the difference of the energies of the electron in the two states. Thus, light of wavelength equal to the lines in the Lyman series will be absorbed.

Q.6: How are x-rays different from visible radiations?
Ans: Both x-rays and visible radiations are electromagnetic waves, but x-rays differ from the visible radiations in the following features:
i. X-rays are highly penetrating. They can pass through many opaque solids such as wood or flesh but are stopped by bones and metals. Hence x-ray photographs are used in medicine.
ii. They cause ionization in gases.
iii. They can eject photoelectrons on striking some metals.
iv. They produce fluorescence in many substances like zinc sulphide, barium platinocyanide, etc.
v. They can damage living tissues if exposed to them for a longer duration.

Q.7: What property of x-rays makes them so useful in seeing otherwise invisible internal structures?
Ans: In solids, the atoms are grouped together in a regular manner. The interatomic distance in a crystal is of the order of the wavelength of x-rays. Hence a crystal is used as a 'transmission grating' to produce diffraction of x-rays. This x-ray crystallography has helped to locate the internal structure of crystal systems (called basic unit cells). Recently developed internal imaging devices (for the human body) include CT (computerized tomography) scanning, MRI (Magnetic Resonance Imaging), and PET (Positron Emission Tomography).

Q.8: Explain the difference between laser light and light from an incandescent lamp (or bulb)?
Ans:

Laser Light	Incandescent Light
i. Laser light is highly monochromatic.	i. Light from an incandescent bulb is a mixture of several wavelengths.
ii. It consists of parallel waves in a narrow beam and is highly directional (i.e., moves straight without spreading).	ii. It is emitted in all directions and spreads out.
iii. It is produced due to stimulated emission of radiation.	iii. It is produced due to spontaneous emission of radiation.

Q.9: Does the light emitted by a neon sign constitute a spectrum or only a few colors? Explain?
Ans: The luminous neon in a discharge tube has a reddish color. Its spectrum is composed of a few colors (line spectrum) of wavelength, very close to each other. So the spectral lines are closely spaced to form a band spectrum.

Q.10: Suppose you are given a glass tube having two electrodes sealed on both ends. The inside is either hydrogen or helium. How can you tell which one it is without breaking the tube?
Ans: The electrodes are connected across a voltage source. If the voltage is gradually increased, then the hydrogen-filled tube will become luminous first because its ionization potential is four times less than that of helium.

The gases can also be differentiated by taking the spectrum of each other.

Q.11: The hydrogen atom contains only a single electron and yet the hydrogen spectrum contains many lines. Why is this so?
Ans: The atoms of hydrogen can be excited to different energy levels. The excited electrons will not stay there. These will jump to the inner orbits. On de-excitation, an electron does not necessarily return to the ground state in a single jump. Rather, it may return by several jumps. Thus, several spectral lines of different frequencies are emitted, depending upon the differences of energies between the levels for the transitions. So, the spectrum of hydrogen contains many lines.

Q.12: The electron in a hydrogen atom requires energy of 10.2eV for the excitation to a higher energy level. A photon and an electron, each of energy 10.5eV, are incident on the atom. Which of these can excite the atom? Give an explanation in support of your answer.
Ans: To excite an electron, energy can be supplied to the electron by direct collision with accelerated particles as well as by the photons of energy hv. The energy of a photon must be exactly equal to the excitation energy (10.2 eV) for the bound electron; otherwise, it will not be absorbed (since it cannot transfer its energy in parts).

On the other hand, accelerated particles can give energy to the bound electron in full as well as in part. Hence an electron 10.5eV (a little higher than the excitation energy of 10.2 eV) can excite the hydrogen atom.

Q.13: Describe the atomic processes in the target of an x-ray tube whereby x-ray continuous spectra and characteristic spectra are produced?
Ans: The x-rays produced by an x-ray tube consist of two parts:
i. A series of un-interrupted wavelengths having a short cut-off wavelength (Xm) are produced when high-velocity electrons are decelerated by a heavy nucleus. This constitutes a continuous spectrum of photons, including x-rays. This process is called 'bremsstrahlung' (German for breaking radiation).
ii. A number of distinct and discreet wavelengths which constitute line (or discontinuous) spectrum of the x-rays are produced when electrons are dislodged from the inner most orbits, followed by electron jumps from the outer orbits. So characteristic spectra result from transitions to a 'hole' in an inner energy level.

Q.14: Explain clearly why x-ray emission lines in the range of 0.1nm are not observed from an x-ray tube when a low atomic number metal is used as the target in the tube?
Ans: For the production of most energetic x-rays, the electrons must be raised from deploying energy levels of the target atoms and certain electrons of innermost shell must be knocked out. The target metal with low atomic number will have x-rays of larger wavelengths. Hence, emission lines of x-rays in the range of 0.001 - 1 nm are not observed.

Q.15: Why do the frequencies of characteristic x-rays depend on the type of the material used for the target?
Ans: The transitions for the emission of characteristic x-rays depend upon the nature of the target material atoms, because frequency of x-rays (v) depends upon the atomic number (z) of the target material [v proportional z-according to Moseley’s law: v: (2.48 x 10^15 Hz) (Z - 1)^2]. Due to Moseley’s work, the characteristic x-ray spectrum became the universally accepted signature of an element.

Q.16: Does the maximum frequency in the ‘bremsstrahlung process’ depend on the nature of the target material?
Ans: No. the maximum frequency and minimum wavelength in the ‘bremsstrahlung process’ do not depend on the material.

Q.17: In laser operation, what process is required to be produced before ‘stimulated emission’?
Ans: Laser operation requires the creation of a non-equilibrium condition, called “population inversion” in which the number of atoms in a high energy state is greater than the number in a lower energy state.

Q.18: Why does laser usually emit only one particular color of light rather than several colors?
Ans: A laser beam is highly coherent and monochromatic, i.e., the emitted photons have the same frequency and wavelength. As each and every color has its own wavelength, so a laser, being monochromatic, emits only one particular color of light.

Advent of Modern Physics - Question Answers - Physics XII

ADVENT OF MODERN PHYSICS

Chapter - 17

Q.1: What do you understand by a frame of reference? What is the difference between inertial frame and non-inertial frame?
Ans: The position and motion of a body can be located with reference to some coordinate system, called the frame of reference.

The frame of reference that is either at rest or moves with uniform velocity is called an inertial frame. It has zero linear or rotational acceleration. Newton’s laws hold well in such a frame. All inertial frames of references are equivalent.

The frame of reference which possesses acceleration is known as a non-inertial frame. Laws of motion do not remain valid in such a frame.

Q.2: Explain why the Compton Effect is not observable with visible light?
Ans: In Compton’s experiment of x-rays of wavelength - 1 Å, equivalent to energy - 140 eV, were directed on a graphite block, where binding energies of bounded electrons were 102 eV. If visible light is used, it possesses low frequency, and these photons have energies - 0.1 eV. This energy is too small to be given to loosely bound electrons to get them scattered.

Q.3: What phenomena require wave description of light? What phenomena required particle picture of light? How are the two aspects related putatively?
Ans: The convincing evidences that light are a wave phenomena are:

Interference of light
Diffraction of light
Polarization of light
Production of electromagnetic waves
The optical Doppler Effect.

The idea of quantum nature of light, i.e., photon (which has a particle nature), was introduced due to the following evidences:

Black body radiation
The photoelectric emission
Compton scattering
X-ray production

The wave and particle aspects are related in de Broglie equation as: $λ = \frac{h}{m v}$ . Thus a particle of non-zero rest mass moves as if it were guided by an associated matter wave. Nevertheless, the ‘particle waves’ are waves of probability. Confirmation of de Broglie wavelength came in 1927 by C.J. Division and L.H. German and, independently, G.P. Thomson. It is astounding to note that Thomson (J.J.), the father, was awarded the Nobel prize in 1906 for having shown that the electron is a particle; and 31 years later Thomson (J.P.), the son, for having shown that the electron is a wave.

Q.4: In what way do the particles of light (photons) differ from the particles of matter, such as electrons and protons?
Ans:
Particles of matter (e.g., electron, proton, etc.) possess certain characteristics:

Non-zero rest mass.
They possess inertia and contain no energy 'packets.'
Their speed is always less than $c$ (speed of light).
Their energy is proportional to the square of the speed ( $E = \frac{1}{2} m v^{2}$ ).
They may be charged or uncharged.
When in motion, they are guided by matter waves.

Particles of light (photons) possess the following distinct characteristics:

Zero rest mass.
They consist of waves in packets of discrete amounts (called 'energy packets' or quanta).
They travel with speed equal to that of light.
Their energy is proportional to frequency ( $E = h ν$ ).
They are always electrically neutral.
They are not guided by matter waves.

Q.5: In the photoelectric effect, the energy of a photoelectron is less than that of an incident photon. Explain?
Ans: When radiation (a photon) strikes a metal surface, it deposits its entire energy on some electron in the absorbing surface. If the energy of the photon (by $h ν$ ) exceeds the energy required by the electron in work against the force binding it to the surface ( $ϕ_{0}$ ), it will be emitted with some energy. As $K . E . = h ν - ϕ_{0}$ , hence $k . e . < h ν$ .

Q.6: How did de Broglie hypothesis help to explain the stability of the atom?
Ans: According to de Broglie's hypothesis, an electron moving around the nucleus is pictured as a kind of wave packet (standing wave). An electron can circle a nucleus indefinitely without radiating energy provided that its orbit contains an integral number of de Broglie wavelengths.

Q.7: What is rest mass of a body?
Ans: Rest mass ( $m_{0}$ ) is the mass of a body when it is at rest with respect to an observer. The relativistic mass of a body moving with certain velocity $v$ is given by

$m = \frac{m_{0}}{\sqrt{1 - \frac{v^{2}}{c^{2}}}}$

Q.8: If we keep applying a force on a material object, can the object gain the speed of light?
Ans: If we keep applying a force which can produce a velocity equal to the velocity of light ( $v = c$ ), then the mass of the material body would become infinite. This is not possible.

Q.9: A block of polished metal having a black spot in the middle is heated above 3000 K and then placed in a dark room. Write your observations?
Ans: If a metal block is heated to incandescence at about 1000K, the metal has a dull red glow. A further high temperature changes into orange, then yellow and finally to white (3000 K) the black spot behaves as a black body. It absorbs maximum energy and appears as black. When seen in a dark room, the black spot radiates more energy (since a good emitter is a good emitter) than the rest of the block. The black spot appears brighter than the rest of the surface.

Q.10: Does the fact that an atom can emit a photon violate the law of conservation of energy? Explain?
Ans: No. An atom in an excited state can emit a photon. The energy received in jumping up is released in the emission.

Q.11: Can matter (e.g., electron) be created or destroyed?
Ans: Matter can be created from energy (photon) in pair production; and can be destroyed as photons in annihilation of matter process.

Q.12: Can pair production take place in vacuum? Explain
Ans: No, because this process requires a heavy nucleus to conserve momentum and energy of the system. The heavy nucleus takes the recoil after stopping the photon.

Q.13: Can an intense beam of television waves focused on a metal cause photoemission?
Ans: No, because TV waves are of low frequency, while a metal requires high threshold frequency for photoemission.

Q.14: Both photoelectric emission and Compton scattering are processes that involve interaction of radiation with matter. How do they differ?
Ans: In photoelectric effect, a low energy photon (e.g., ultraviolet light) can lose all its energy on striking an electron, and the photon vanishes. But in Compton Effect, a high energy photon (e.g., X-ray) loses part of energy and a photon is scattered with the remaining energy (and hence frequency decreases).

Q.15: The speed limit of our highways is 65 km/h. If the speed of light were the same, would you be able to drive at the speed limit?
Ans: No, because mass would become infinite.

Q.16: A ball is dropped from a helicopter flying at constant speed horizontally. Describe its motion relative to the pilot and an observer on earth’s surface.
Ans: According to the observer on the earth, it will fall forward towards the ground following a projectile path.

According to a pilot, it will to a point on the earth vertically.

Q.17: Why does the casing of a large electric transformer have metal blades fastened to it perpendicular to the surface and painted black?
Ans: The blades transfer heat by radiation to the atmosphere by increasing the surface area. They are painted black because black body radiates energy at a faster rate.

Electromagnetic Waves and Electronics - Question Answers - Physics XII

Chapter - 16

Q.1: Under what circumstances does a charge radiate electromagnetic waves?
Ans: A charge radiates electromagnetic (e.m.) waves when it is accelerated.

Q.2: In an electromagnetic wave, what is the relationship, if any, between the variation in the magnetic and electric fields?
Ans: In an electromagnetic wave, the transverse sinusoidal oscillating electric field and magnetic field are propagated at right angles to each other and to the direction of motion.

Q.3: A radio transmitter has a vertical antenna. Does it matter whether the receiving antenna is vertical or horizontal?
Ans: A receiving antenna should be vertical just like a transmitting antenna. A horizontal receiving antenna will intercept much less radio frequency signals.

Q.4: Explain why are light waves able to travel through a vacuum, whereas sound waves cannot?
Ans: Light waves are electromagnetic waves (of wavelength 400 nm to 760 nm). Sound waves are produced due to the vibration of the molecules of a medium. Hence, sound waves require a material medium, whereas light waves do not require a medium for their propagation.

Q.5: Explain the condition under which radiation of electromagnetic waves takes place from a certain source?
Ans: When a transmitting antenna is coupled with an alternating source of potential (known as oscillator), charges (electrons) are accelerated up and down the antenna. This creates a fluctuating electric flux, which generates a magnetic flux. Hence the waves propagated from an antenna are electromagnetic waves.

Q.6: Can a diode be used for amplifying a weak signal?
Ans: Normally, a diode cannot be used for amplifying a weak signal. But specially constructed diode (e.g., tunnel diode) can be used as an amplifier and oscillator for microwave frequencies.

Q.7: Are radio waves form of light?
Ans: Since both radio waves and visible light are electromagnetic in nature, hence we can say that radio waves are a form of light (of frequency 4 x $10^{14}$ Hz), having frequencies much lower (30 kHz to 300 MHz) than light.

Q.8: Can e.m. waves be propagated through a piped vacuum?
Ans: Yes.

Q.9: Why does a semiconductor act as an insulator at 0K and why does its conductivity increase with an increase in temperature? OR - Discuss the effect of temperature on semiconductors?
Ans: In a semiconductor, at 0K, the valence band is completely filled and the conduction band is totally empty. The semiconductor, therefore, behaves like a perfect insulator. At room temperature, some of the electrons in the valence band gain energy from thermal agitation of the lattice atoms and move up into the conduction band, leaving holes in the valence band. If the temperature is increased, due to further thermal agitation, more electrons occupy the conduction band. Thus, the conductivity of the semiconductor increases with an increase in temperature.

Q.10: Explain the role of forbidden band in solids?
Ans:

In conductors, the conduction band and valence bands are overlapping and hence no forbidden band exists.
In insulators, the conduction and valence bands are separated by a large forbidden band.
In semiconductors, the conduction and valence bands are separated by a small forbidden energy gap.

Q.11: Why is light not seen in an ordinary diode but an LED emits light?
Ans: Silicon is opaque to light. So, an ordinary silicon diode does not emit light, but an LED is a junction diode made from gallium arsenide phosphate crystal. When it is forward biased, electron-hole recombination takes place, which results in the release of light.

ELECTRICAL MEASURING INSTRUMENTS

Chapter - 15

Q.1: What is the function of the concave pole pieces and the coaxial soft iron cylinder in the moving coil galvanometer?
Ans: The concave magnetic poles and the cylindrical core make the magnetic field radial and stronger (so the current becomes directly proportional to the deflection).

Q.2: Why is it necessary to have some form of controlling couple in the moving coil galvanometer?
Ans: Controlling couple is necessary to control the motion of the coil, it is proportional to the current to be measured. It is produced by using a spring control method, which consists of two hair springs attached to a spindle wound in the opposite directions. As the coil rotates the spring winds up and produces a counter torque. The coil comes to rest (the final deflection of the pointer is given) when the deflecting torque (or magnetic torque) is counterbalanced by the controlling torque (or restoring torque).

Q.3: What is meant by the sensitivity of a galvanometer? On what a factor does it depend? How can we have large sensitivity of a moving coil galvanometer?
Ans: A galvanometer is sensitive if it gives large deflection for a very small current. The sensitivity of a galvanometer is the current in microamperes required to cause a deflection of 1mm or 1 division.

S = \frac{I (\text{in } \mu A)}{\theta (\text{in div})}

Since $I = K \cdot \theta$ , hence the galvanometer is sensitive if $K (= C/BAN)$ is small. Sensitivity depends on $C$ (couple per unit twist), $N$ (number of turns), $A$ (area of coil) and $B$ (strength of magnetic field).

For large sensitivity a soft iron core (sphere or cylinder) is placed inside the coil and the poles are made circular or cylindrical. This makes $4B$ stronger and radial.

Q.4: Which galvanometer usually has greater sensitivity, aluminum pointer or lamp and scale type? Why?
Ans: Lamp and scale type galvanometer has greater sensitivity ( $10^{-15}$ A/div), because it gives large deflection for a very small current.

Q.5: We want to convert a galvanometer into (a) an ammeter (b) a voltmeter. What do we need to do in each case?
Ans:

To convert a galvanometer into an ammeter, we connect a low resistance in parallel (called shunt).
To convert a galvanometer into a voltmeter, we connect a high resistance in a series (called multiplier).

Q.6: Why is it necessary for an ammeter to have zero or negligibly small resistance?
Ans: An ammeter must have negligibly small resistance so that it may not alter the current being measured.

Q.7: What necessary condition must a voltage measuring device satisfy?
Ans: A voltage measuring device must contain a very high (in fact, infinite) resistance, so that it will, practically, draw no current from the circuit across which it is connected.

Q.8: Why must an ammeter be connected to a circuit in series and a voltmeter in parallel?
Ans: An ammeter must be connected in series to a circuit because its resistance is very small as compared to the total resistance of the circuit. Hence it does not alter the current being measured. But a voltmeter has very high resistance, so it must be connected in parallel to a circuit.

Q.9: An ammeter and voltmeter of suitable ranges are to be used in a circuit. What might happen if by their mistake positions are interchanged?
Ans:

If, by a mistake, an ammeter is connected in parallel to a circuit, its coil will be burnt out to heavy current (because of its extremely low resistance).
When a voltmeter, by mistake, is connected in series to a circuit it will give reading but will not record correct p.d. because it will decrease the current (due to its very high resistance). It will not cause damage.

Q.10: The terminals of ammeters are usually made of thick and bare metal while those of voltmeters are quite thin and well insulated. Explain why?
Ans:

An ammeter must have very low resistance. So its terminals should have almost zero resistance. Hence terminals must be made of thick, bare metal.
A voltmeter must have very high resistance. So its terminals should be thin and well insulated to avoid sparking between the terminals.

Q.11: Why is a potentiometer considered one of the most accurate voltage measuring devices?
Ans: The principle of a potentiometer is that the potential drop across any length of wire of uniform cross-section is directly proportional to the length of the wire. At the balance point, the two terminals of the galvanometer are at the same potential, and no current will flow through it. Hence, a potentiometer is an instrument that can be used to measure the emf of a source and compare potentials without drawing any current from the source. Essentially, it balances an unknown p.d. against an adjustable, measurable p.d.

Q.12: How is a Wheatstone bridge used for measuring an unknown resistance?
Ans: If we connect three resistances $R_1$ , $R_2$ , and $R_3$ of precisely known adjustable values and a fourth unknown resistance $R_4$ , and these are so adjusted that the galvanometer shows no deflection; then in this balanced condition, $R$ square root $R_2$ is equal to $R_3$ square root $R_4$ . Hence $R_4$ can be calculated.

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