Chapter Exam

Unit 15: Electromagnetic Waves — Online MCQ Test

Q: The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is:

Answer: A. 1:1 — In an electromagnetic wave, the average energy density of the electric field is equal to the average energy density of the magnetic field, meaning each contributes equally to the total intensity.

Q: The electric field in a plane electromagnetic wave is given by Ez = 60 cos (5x + 1.5 × 10^9 t) V/m. Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field):

Answer: A. By = 2 × 10^–7 cos (5x + 1.5 × 10^9 t)T — B = E/c. 60/(3*10^8) = 2*10^-7. Since E is along z and propagation is along x, B must be along y to satisfy E x B = c.

Q: Out of the following options which one can be used to produce a propagating electromagnetic wave?

Answer: C. An accelerating charges — According to Maxwell's theory, an accelerating electric charge creates time-varying electric and magnetic fields, which propagate as an electromagnetic wave.

Q: Out of the following options which one can be used to produce a propagating electromagnetic wave?

Answer: C. An accelerating charges — According to Maxwell's theory, an accelerating charge produces electromagnetic waves.

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Unit 15: Electromagnetic Waves — Important Questions & Answers (FAQ)

Frequently asked questions from NEET NEET (All) PHYSICS — Unit 15: Electromagnetic Waves, with answers and explanations. These are sample questions; the exam has its own separate question set.

The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is:

A. 1:1 ✓
B. 1:c
C. 1:c^2
D. c:1

Answer: A. 1:1
In an electromagnetic wave, the average energy density of the electric field is equal to the average energy density of the magnetic field, meaning each contributes equally to the total intensity.

The electric field in a plane electromagnetic wave is given by Ez = 60 cos (5x + 1.5 × 10^9 t) V/m. Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field):

A. By = 2 × 10^–7 cos (5x + 1.5 × 10^9 t)T ✓
B. Bx = 2 × 10^–7 cos (5x + 1.5 × 10^9 t)T
C. Bz = 60 cos (5x + 1.5 × 10^9 t)T
D. By = 60 sin (5x + 1.5 × 10^9 t)T

Answer: A. By = 2 × 10^–7 cos (5x + 1.5 × 10^9 t)T
B = E/c. 60/(3*10^8) = 2*10^-7. Since E is along z and propagation is along x, B must be along y to satisfy E x B = c.

Out of the following options which one can be used to produce a propagating electromagnetic wave?

A. A stationary charge
B. A chargeless particle
C. An accelerating charges ✓
D. A charge moving at constant velocity

Answer: C. An accelerating charges
According to Maxwell's theory, an accelerating electric charge creates time-varying electric and magnetic fields, which propagate as an electromagnetic wave.

The property which is not of an electromagnetic wave travelling in free space is that;

A. they travel with a speed equal to 1/√(μ0ε0)
B. they originate from charges moving with uniform speed. ✓
C. they are transverse in nature.
D. their energy density in electric field is equal to energy density in magnetic field.

Answer: B. they originate from charges moving with uniform speed.
Electromagnetic waves are produced by accelerating charges, not charges moving with uniform speed. The other statements are true for EM waves in free space.

Out of the following options which one can be used to produce a propagating electromagnetic wave?