Electromagnetic Waves

Question 1

The electric field in a plane electromagnetic wave is given by Ez = 60 cos(5x + 1.5 x 10⁹ t) V/m. Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field):

Accepted Answer

By = 2 x 10⁻⁷ cos(5x + 1.5 x 10⁹ t) T. In a plane electromagnetic wave E and B oscillate in phase with amplitudes related by B₀ = E₀/c, so B₀ = 60/(3 x 10⁸) = 2 x 10⁻⁷ T. E points along z and the wave travels along −x, so B must lie along y — which rules out the other three options.

Answer

Bx = 2 x 10⁻⁷ cos(5x + 1.5 x 10⁹ t) T

Answer

Bz = 60 cos(5x + 1.5 x 10⁹ t) T

Answer

By = 60 sin(5x + 1.5 x 10⁹ t) T

Question 2

A parallel plate capacitor made of circular plates is being charged such that the surface charge density on its plates is increasing at a constant rate with time. The magnetic field arising due to displacement current is:

Accepted Answer

Non-zero everywhere with maximum at the imaginary cylindrical surface connecting peripheries of the plates. A surface charge density growing at a constant rate means a constant displacement current, which sets up a magnetic field exactly as a uniform current-carrying cylinder would. B therefore rises linearly from zero on the axis to a maximum at the plate edge, then falls off as 1/r outside.

Answer

Zero at all places

Answer

Constant between the plates and zero outside the plates

Answer

Zero between the plates and non-zero outside

Question 3

The following table presents parts of the electromagnetic spectrum and their corresponding major applications. The correct option is: P. Microwave Q. UV rays R. Gamma rays S. Radio wave I. For purifying the water II. For warming the food III. For AM and FM communication systems IV. For treating the Cancer cells

Accepted Answer

P-II, Q-I, R-IV, S-III. Microwaves are strongly absorbed by water molecules, which is what heats food. UV is germicidal and is used to purify water. Gamma rays carry enough energy to destroy malignant tissue and are used in radiotherapy. Radio waves are the carriers for AM and FM broadcasting. That gives P-II, Q-I, R-IV, S-III.

Answer

P-I, Q-II, R-III, S-IV

Answer

P-I, Q-IV, R-II, S-III

Answer

P-II, Q-IV, R-III, S-I

Q1.The electric field in a plane electromagnetic wave is given by Ez = 60 cos(5x + 1.5 x 10⁹ t) V/m. Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field):

Q2.A parallel plate capacitor made of circular plates is being charged such that the surface charge density on its plates is increasing at a constant rate with time. The magnetic field arising due to displacement current is:

Q3.The following table presents parts of the electromagnetic spectrum and their corresponding major applications. The correct option is: