MEASUREMENT Chapter # 02 Physics 10th - Question Answers

 Physics 10th - Question Answers

MEASUREMENT
Chapter # 02

Q.1: What is measurement? What is the importance of measurement?

Ans: MEASUREMENT:
The meaning of measurement is the comparison of an unknown quantity with a standard, to see how many times it is big or small as compared to the standard.

Importance Of Measurement:
In our daily life, we get knowledge of things through our five senses: touch, smell, taste, sight, and hearing. However, our senses often do not provide us with correct information.

We use measuring devices generally called apparatus to get the correct measurement. To measure volume, we use a measuring cylinder. For mass, we use a common balance, and for the measurement of length, a meter scale is used. A vernier caliper can measure correctly up to 0.1 mm, and a micrometer screw gauge can measure correctly up to 0.1 mm. Any instrument whose calibration is in doubt must be checked or discarded.

Q.2: Define physical quantities? Write down its types?

Ans: PHYSICAL QUANTITIES:
Every material object has certain characteristics. These are to be measured to specify them. For instance, if we want to specify the characteristics of a brick, we will have to measure its length, width, height, and mass. Such characteristics are called physical quantities.

TYPES OF PHYSICAL QUANTITIES:
Scientists have divided all physical quantities into two groups:

• Fundamental quantities
• Derived quantities

Fundamental Quantities:
Fundamental quantities like length, mass, and time are supposed to be the main physical quantities. All physical quantities in mechanics can be expressed in terms of fundamental quantities.

Derived Quantities:
The physical quantities that are derived from fundamental quantities are called derived quantities. The derived quantities are obtained from simple multiplication and division of fundamental quantities.

Q.3: Write down the name of fundamental quantities in S.I. system?

Ans: There are seven fundamental quantities in the S.I. unit system (International System of Units). Seven basic quantities are:

• Time
• Mass
• Temperature
• Luminous intensity
• Length
• Amount of substance
• Current

Q.4: Write down the fundamental quantities with their units in S.I. system and their symbols?

Ans: THERE ARE FUNDAMENTAL QUANTITIES WITH THEIR UNITS AND SYMBOLS:

Quantity	Unit	Symbols
Length	Meter	m
Mass	Kilogram	kg
Time	Second	s
Temperature	Kelvin	K
Current	Ampere	A
Amount of substance	Mole	mol
Luminous intensity	Candela	cd

Q.5: Write down some derived quantities with their units and symbols?

Ans: THERE ARE SOME DERIVED QUANTITIES WITH THEIR UNITS AND SYMBOLS AS:

Quantity	Unit	Units	Symbols
Speed	meter/second	m/s	v
Volume	cubic meter	m³	V
Acceleration	meter/second²	m/s²	a
Force	Newton	N	F
Pressure	Pascal	Pa	P
Work	Joule	J	W
Charge	Coulomb	C	Q

Q.6: What is a system of units? How many systems of units are there?

Ans: SYSTEM OF UNITS:
A set of fundamental and derived units is called a system of units.

TYPES OF SYSTEM OF UNITS:
There are four systems of units being used in scientific work.

• M.K.S System:
  In MKS system, length, mass, and time are fundamental quantities, and their units are meter, kilogram, and second.

• C.G.S System:
  In CGS system, the fundamental quantities are length, mass, and time, and their units are in this system are centimeter, gram, and second.

• F.P.S System:
  In FPS system, the fundamental quantities are length, force, and time, and their units are foot, pound, and second. It is also called the British Engineering System.

Basic S.I. Units:
In S.I. units, seven quantities are taken as fundamental quantities, which are:

• Length
• Mass
• Time
• Current
• Temperature
• Luminous intensity
• Amount of substance

Q.7: Define standard of mass – kilogram?

Ans: KILOGRAM:
One kilogram is the mass of a platinum-iridium alloy cylinder, which is kept at the International Bureau of Weights and Measures near Paris.

Multiples and sub-multiples are given below:
1 kilogram

$$=1kg=1000gm=10^{3}gm$$

1 gram

$$=1gm=\frac{1}{1000}kg=10^{-3}kg$$

1 gram

$$=1gm=1000mg=10^{3}mg$$

1 milligram

$$=1mg=\frac{1}{1000}gm=10^{-3}gm$$

1 microgram

$$=1\mu gm=10^{-6}gm$$

1 nanogram

$$=1ng=10^{-9}gm$$

1 micro micro gram

$$=1\mu \mu gm=10^{-12}gm$$

Q.8: Give some important masses which was calculated by scientists?

Ans: SOME MEASURED MASSES:

Known Universe	$10^{53}kg$
Our Galaxy	$2\times 10^{43}kg$
The Sun	$2\times 10^{30}kg$
Earth	$6\times 10^{24}kg$
Moon	$7\times 10^{22}kg$
Speck of dust	$7\times 10^{-10}kg$
Virus	$1\times 10^{-15}kg$
Uranium atom	$4\times 10^{-26}kg$
Proton	$2\times 10^{-27}kg$
Electron	$9\times 10^{-31}kg$

Q.9: Define standard of length - meter?

Ans: STANDARD OF LENGTH - METER:
The meter is the length of the path traveled by light in vacuum during a time interval of $\frac{1}{299,792,458}$ of a second.

OR
It is also defined as a distance between two marks engraved on an iridium-platinum alloy bar kept at the International Bureau of Weights and Measures near Paris.

Multiples and sub-multiples are given as:
1 kilometer

$$=1km=1000m=10^{3}m$$

1 meter

$$=1m=\frac{1}{1000}km=10^{-3}km$$

1 meter

$$=1m=100cm=10^{2}cm$$

1 centimeter

$$=1cm=\frac{1}{100}m=10^{-2}m$$

1 millimeter

1millimeter=1mm=10001​m=10−3m

1 centimeter

$$=1cm=10mm$$

Q.10: Give some important lengths which were calculated by scientists?

Ans: SOME MEASURED LENGTHS:

Object	Measured Length
Farthest observed quasar	$2\times 10^{26}m$
Andromeda galaxy	$2\times 10^{22}m$
Radius of galaxy	$6\times 10^{19}m$
The nearest star (Proxima Centauri)	$4\times 10^{16}m$
The orbit radius of planet Pluto	$6\times 10^{12}m$
Radius of the sun	$7\times 10^{8}m$
Radius of the earth	$6\times 10^{6}m$
Radius of hydrogen atom	$5\times 10^{-11}m$
Effective radius of proton	$2\times 10^{-15}m$

Q.11: Define standard of time - second?

Ans: STANDARD OF TIME - SECOND:
It is defined as the duration in which a cesium atom of mass number 133 completes 9,192,631,770 vibrations.

Multiples and sub-multiples are given below:
1 minute (min)

$$=60s(\text{seconds})$$

1 hour (h)

$$=60\text{minutes}=60\times 60s=3600s$$

1 minute (min)

$$=\frac{1}{60}h$$

1 second (s)

$$=\frac{1}{60}\text{min}=\frac{1}{3600}h$$

1 millisecond (ms)

$$=\frac{1}{1000}s=10^{-3}s$$

1 microsecond (µs)

$$=\frac{1}{1,000,000}s=10^{-6}s$$

1 nanosecond (ns)

=1,000,000,0001​=10−9s

Q.12: Give some important times which were calculated by scientists?

Ans: SOME MEASURED TIMES:

Event	Measured Time
Lifetime of proton	$>10^{40}sec$
Age of universe	$5\times 10^{17}sec$
Time of earth’s orbit around the sun (1 year)	$3\times 10^{7}sec$
Time of earth’s rotation about its axis (1 day)	$9\times 10^{4}sec$
Time between normal heartbeats	$8\times 10^{-1}sec$
Period of oscillation of 3 cm microwave	$1\times 10^{-10}sec$
Lifetime of least stable particles	$<1\times 10^{-23}sec$

Q.13: What are the advantages of S.I. units?

Ans: ADVANTAGES OF S.I. UNITS:

• It makes calculations easier because smaller and bigger units can be obtained just by a simple division or multiplication by a factor of ten.
• For larger and smaller quantities, we can use prefixes with the units.
• Prefixes for factors greater than unity have Greek roots.
• Prefixes for factors less than unity have Latin roots.

Q.14: Give some S.I. prefixes?

Ans: S.I. PREFIXES:

Factors	Prefixes	Symbols
$10^{18}$	exa	e
$10^{15}$	peta	p
$10^{12}$	tera	t
$10^9$	giga	g
$10^6$	mega	m
$10^3$	kilo	k
$10^2$	hecto	h
$10^1$	deka	da
$10^{-1}$	deci	d
$10^{-2}$	centi	c
$10^{-3}$	milli	m
$10^{-6}$	micro	$\mu$
$10^{-9}$	nano	n

| $10^{-12}$ | pico | p | | $10^{-15}$ | femto | f | | $10^{-18}$ | atto | a |

Q.15: What are significant figures or digits in a number or reading? What are the rules for determining significant figures in a number?

Ans: NUMBER OF SIGNIFICANT FIGURES IN A NUMBER OR READING:
If any measurement, the accurately known digits and the first doubtful digit are called significant figures of that number.

Rules for determining significant figures of a number:

• All non-zero digits are significant, e.g., 123 has three significant figures: 1, 2, and 3.
• Zero appearing between non-zero digits are significant, e.g., 7003, 40.71, and 2.503 all have four significant figures.
• Zero appearing in front of all non-zero digits are not significant. They act as placeholders, e.g., 0.0081, 0.56, 0.00033 all have two significant figures.
• Zeros at the end of a number and to the right of a decimal point are significant, e.g., 65.00, 2.010, 7.000 all have four significant figures.
• Zero at the end of a number and to the left of the decimal point (number greater than 1) can be confusing. They are not significant if they just serve as placeholders for the magnitude of the number. The zeros in 300, 900, and 2821 may or may not be significant. To avoid ambiguity, the measurement should be written in standard exponential form (scientific notation), e.g., 3.00 × 10², 7.00 × 10³, and 2.7210 × 10³. In these examples, the numbers of significant figures are three, four, and five, respectively.

Q.16: What is scientific notation?

Ans: SCIENTIFIC NOTATION:
Scientists often work with very large and very small measurements. For example, the mass of the earth is about 6,000,000,000,000,000,000,000,000 kg. In this form, the measurement takes up much space and is difficult to use in calculations. To work with such measurements more easily, we can write them in a shortened form by expressing decimal places as powers of ten. This method of expressing numbers is called exponential notation. Scientific notation is based on exponential notation. In scientific notation, the numerical part of a measurement is expressed as the product of a number between 1 and 10 and a whole number power of ten:

$$M\times 10^n$$

In this expression, $1\le M<10$ and $n$ is an integer. For example, two kilometers can be expressed as $2\times 10^{3}m$.

Q.17: What is vernier callipers? What are its major parts?

Ans: VERNIER CALLIPERS:
Vernier callipers is a meter stick graduated in millimeters used to measure a distance up to 1 mm. It can also be used to measure a distance up to 0.05 mm.

PARTS OF VERNIER CALLIPERS:
There are four major parts of vernier callipers:

• Main scale
• Vernier scale
• Jaws
• Thin flat rod

Main Scale:
A vernier calliper consists of a rectangular steel bar whose one side is graduated in millimeters. Each division on the main scale is 1 mm (0.1 cm).

Vernier Scale:
A small scale usually consisting of 10 divisions which slides over the main scale is known as the vernier scale.

Jaws:
There are two jaws present on a vernier calliper, which is also called callipers. One is called the upper jaw and the other is called the lower jaw.

Thin Flat Rod:
A thin flat rod is attached to the sliding scale on its back, which can measure the internal depth of a hollow cylinder.

Q.18: Write down the construction and working of vernier callipers?

Ans: CONSTRUCTION OF VERNIER CALLIPERS:
Vernier callipers consist of two parts. The first part consists of a scale called the main scale. The longer lines on the main scale represent centimeters and smaller lines, millimeters. Its left upper part has a jaw “A”. The second part consists of a vernier scale, which can slide over the main scale. The left upper part of this scale has a jaw “B”. Jaw “A” is fixed while jaw “B” is movable.

Working Of Vernier Callipers:
The diameter of a small spherical object can be measured with the help of this device. Before the measurement, close the jaws of the vernier calliper completely and note down whether the zero line of the vernier scale coincides with the zero of the main scale. If they coincide, there is no zero error. Open the jaws now and place an object between them. Read the scale division to the left of the zero of the vernier scale and also read the reading.of vernier scale, note it down in the observation table. Again, place the cylinder in between the jaws to measure the diameter. Read the main scale and vernier scale reading, note down in the observation table. Repeat the same three times.

Q.19: Draw the neat and labeled diagram of vernier callipers and show all the major parts on it?

Ans: DIAGRAM:

(Diagram of Vernier Callipers with labels)

• Outside Jaws
• Inside Jaws
• Cylinder
• Main Scale
• Vernier Scale

Q.20: Define vernier constant OR least count of vernier callipers? How is it calculated?

Ans: VERNIER CONSTANT OR LEAST COUNT:
The minimum measurement that can be measured by a vernier calliper is called vernier constant or least count (L.C).

CALCULATION OF VERNIER CONSTANT:
Method No 1:

$$\text{Least count}=\frac{\text{Smaller Division on main scale}}{\text{Total No. of Division of V.S}}$$

• When a vernier calliper has 10 divisions:

$$L\mathrm{.}C=\frac{0.1}{10}$$

• When vernier calliper has 20 divisions:

Method No 2:
10 vernier divisions

1 vernier division

1 main scale division

L.C = Difference between 1 main scale division and 1 vernier scale division

Q.21: Define zero error? Write down its types?

Ans: ZERO ERROR:
It is an error which arises when zeroes of the main scale and vernier scale do not coincide with each other upon joining two jaws.

TYPES OF ZERO ERROR:
There are two types of zero error:

• Positive zero error
• Negative zero error

Positive Zero Error:
If the zero of the vernier scale is on the right of the zero of the main scale, the zero error will be positive.
The observed value is more than the actual value, so the difference is to be subtracted from the observed value.

Negative Zero Error:
If the zero of the vernier scale is on the left side, the zero error will be negative. The measured value is less than the actual value, so the difference is to be added to the observed value.

Q.22: Define micrometer screw gauge? Write down its major parts?

Ans: SCREW GAUGE:
It is an instrument that can measure small length thickness correctly up to $\frac{1}{1000}$ of a millimeter or up to three places of decimals.

Major Parts:
There are the following parts of a screw gauge:

• U-shaped metal frame
• Fixed stud
• Movable stud
• Main scale
• Circular scale
• Drum
• Ratchet

Q.23: Draw neat and labeled diagram of screw gauge and show the name of all parts?

Ans: DIAGRAM:

(Labeled diagram of Micrometer Screw Gauge showing Linear Main Scale, Spindle, Sleeve, Thimble, Ratchet, Anvil, and Frame)

Q.24: Define pitch and least count of a screw gauge?

Ans: PITCH OF THE SCREW:
It is the distance between the two consecutive threads of the linear screw. It is measured by the distance traveled by the circular scale on the main scale during one complete rotation of the circular scale.

Least Count Of Screw Gauge:
The least count of the screw gauge is given as:

$$\text{Least count}=\frac{\text{No. of Divisions on the Circular Scale}}{\text{Pitch of the Screw}}$$

For a 50-division screw gauge:

$$L\mathrm{.}C=\frac{1}{50}$$

For a 100-division screw gauge:

$$L\mathrm{.}C=0.002cm$$$$L\mathrm{.}C=\frac{1}{100}=0.01mm$$$$L\mathrm{.}C=0.001cm$$

Q.25: Define zero error of screw gauge and its types?

Ans: ZERO ERROR:
When we close the two studs of the screw gauge, if the zero of the circular scale has advanced beyond the zero line of the main scale or left behind the zero of the main scale, there is zero error.

TYPES OF ZERO ERROR:
There are two types of zero error:

• Positive zero error
• Negative zero error

Positive Zero Error:
If the zero of the circular scale is below the horizontal reference line, the zero error is positive. The observed value is more than the actual value. Note the number of divisions on the circular scale from zero which coincides with the reference line. Multiply this number by the least count. This is positive zero error, which is subtracted from the observed value to get the correct value.

Negative Zero Error:
If the zero of the circular scale is above the reference line and the edge of the drum has crossed the zero line of the main scale, then the zero error is negative. Note the number of divisions on the circular scale that coincide with the reference line. Multiply it by the least count. This is negative zero error. Add this error to the observed value to get the correct measurement.

Q.26: Write down the construction of screw gauge?

Ans: MICROMETER SCREW GAUGE:
A micrometer screw gauge measures very small lengths, such as the diameter of a wire or sphere. It can measure accurately up to one hundredth part of a millimeter.

Construction:
It consists of a U-shaped metallic frame having a fixed stud at A. The other end has a hollow cylinder C. A line is marked on the cylinder parallel to its axis, which has a millimeter scale. This cylinder acts as a nut with a bolt inside it. The right end of the bolt is like a cap. The bolt can be rotated with the help of this cap. The left end of this cap has a scale, which is usually divided into 100 equal parts (50 divisions are also found).

Q.27: Write down the working of a Stop Watch?

Ans: STOP WATCH:
It is a special watch used to measure time intervals for events.

Working:
In normal condition, both hands remain static and indicate zero reading on their dials.

• To note the time, both hands of the stop watch are set at zero by pressing and releasing the knob B.
• As the knob B is pressed and released again, the watch starts.
• When the second hand completes one rotation of sixty seconds, the minute hand advances by one division.
• When we want to stop the watch, the knob B is pressed and released again.
• The new position of the hands gives the time interval for which the stop watch was in operation.

Q.28: What is a measuring cylinder?

Ans: MEASURING CYLINDER:
It is a glass cylinder with a scale graduated in cubic centimeters (cm³) or milliliters (ml). It is used to find the volume of liquids.

When a liquid is poured in it, the liquid level rises to a certain height in the cylinder. The level of the liquid in the cylinder is noted, and the volume of the liquid is obtained.

We should keep the eye level with the bottom of the meniscus of the liquid surface. The cylinder must be on a smooth horizontal table.

Q.29: Define error? Write down its types?

Ans: ERROR:
An error is defined as the difference between the measurement and the actual value.

TYPES OF ERROR:

Personal Error:
Personal error is the error that belongs to the person who is performing the experiment. It may arise due to making an error in reading a scale.

In order to record a reading from a scale, we have to line up the object we are measuring with the scale and hold our eye in one particular position for making a correct observation.

observation. Personal error is minimized by taking some careful precautions or by adopting some proper procedure.

Random Error:
A random error can arise due to external conditions, e.g., the temperature, moisture, or voltage may fluctuate. Such error can be minimized by taking several readings and calculating the mean value.

Systematic Error:
This error arises due to a fault in a measuring instrument. It might be due to a systematic variation and is called zero error. This might also arise due to non-uniform or wrongly marked graduation. We can remove the error by comparing the measuring instrument with a standard instrument. We can also make the zero correction whether it is positive or negative.

Q.30: What is accuracy? How can we ensure accuracy?

Ans: ACCURACY:
It is the measurement of a quantity as close to the factual or real values as possible. We can increase the accuracy of a measurement by controlling and reducing all types of errors.

Ensuring Accuracy:
An easy way of ensuring accuracy is to take a large number of readings of the same measurement and take their average as given below:

The average or mean value of the set of numbers 5.42, 6.18, 5.70, 6.01, 6.32

So,

$$\text{Mean}=\frac{5.42+6.18+5.70+6.01+6.32}{5}$$$$\text{Mean}=5.93$$

Here, the lowest value is 5.42 and the highest value is 6.32. The deviation between these values is 0.9. But the deviation of the individual numbers from the mean or average value is less than 0.90. Thus, the average value is considered close to the real value.

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