CBSE Class 12 Physics Electromagnetic Wave Solved Examples

CBSE Class 12 Physics Electromagnetic Wave Solved Examples. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Ex.1 Elecromagnetic waves travel in a medium with a speed of 2 × 10⁸ m/s. The relative permeability of the medium is 1. What is the relative permittivity of the medium-
Sol. The speed of electromagnetic waves and in a medium is given by

Ex.2 Fig. shows a capacitor made of two circular plates each of radius 12 cm and separated by 5.0 mm. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and equal to 0.15 A.

(b) Displacement current is equal to conduction current i.e. 0.15 A.
(c) Yes, Kirchhoff’s first rule is valid at each plate of the capacitor provided. We take the current to be the sum of the conduction and displacement currents.

Ex.3 A magnetic field in a plane electromagnetic wave is given by By = 2 × 10 ^–7 sin(0.5 × 103x + 1.5 × 1011t) tesla.
(a) What is wavelength and frequency of the wave ?
(b) Write down an expression for the electric field. (x is in metre and t in second.)

Sol. Given

Ex.4 The electric field of a plane electromagnetic wave in vacuum is represented by Ex = 0, Ey = 0.5 cos[2π × 108 (t – x/c)] and Ez = 0
(a) What is the direction of propagation of electromagnetic wave ?
(b) Determine the wavelength of the wave.
(c) Compute the component of associated magnetic field
Sol. (a) The given equation
Ey = 0.5 cos[2π × 108 (t – x/c)] ..... (1)
indicates that the electromagnetic waves are propagating along the positive direction of X-axis.
(b) The standard equation of electromagnetic wave is given by

Ex.5 A light beam travelling in the X-direction is described by the electric field Ey = (300 V/m) sinω(t – x/c). An electron is constrained to move along the Y-direction with a speed of 2.0 × 10⁷ m/s. Find the maximum electric force and the maximum magnetic force on the electron.
Sol. The maximum value of magnetic field (B0) is given by

Ex.6 The TV transmission tower at a particular staion has a height of 160 m.
(a) What is its coverage rang ?
(b) How much population is covered by transmission, if the average population density around the tower is 1200/km².
(c) By how much the height of tower be increased to double its coverage range ?
Sol. (a) We know that