MAGNETISM & ELECTROMAGNETISM

Chapter – 14

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Q.1: What is flux density and how is it related to the number of lines of induction expressed in Webers?
Ans: Magnetic flux density $B$ is the magnetic flux per unit area $(B = \Phi / A)$. The unit of flux density is Weber per $m^2$ (or tesla, $T$). Magnetic flux is the total number of magnetic lines of induction passing perpendicularly through an area $(\Phi = B \times A)$. Its SI unit is ‘Weber’ $(1 Wb = 1 T \cdot m^2)$. Hence magnetic flux density refers to the number of lines of induction (in Webers) per square meter.

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Q.2: Charged particles fired in a vacuum tube hit a fluorescent screen. Will it be possible to know whether they are positive or negative?
Ans: Yes, the charge on particles in motion can be found by applying a magnetic field perpendicular to the motion of the charges and by observing the deflection. A positive charge in an inward perpendicular magnetic field is deflected upward. In an electric field, a positive charge will be deflected towards the negative side (plate).