Chapter Exam

Chapter-8 Electromagnetic Waves — Online MCQ Test

Q: Which equation introduced the concept of displacement current?

Answer: C. Ampère-Maxwell law — Maxwell modified Ampère's law by adding the displacement current term, creating the Ampère-Maxwell law which is fundamental to electromagnetic wave theory.

Q: The relationship between the amplitudes of electric field (E₀) and magnetic field (B₀) in an electromagnetic wave is:

Answer: B. E₀ = cB₀ — The amplitude of the electric field and magnetic field in an electromagnetic wave are related by E₀ = cB₀, where c is the speed of light.

PHYSICS · Grade 12 · CBSE(NCERT)

Practice Chapter-8 Electromagnetic Waves with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 PHYSICS. This chapter covers: electromagnetic waves - displacement current - electromagnetic spectrum - radio waves - gamma rays. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter-8 Electromagnetic Waves — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 PHYSICS — Chapter-8 Electromagnetic Waves, with answers and explanations. These are sample questions; the exam has its own separate question set.

What is displacement current?

A. Current that flows through a dielectric medium
B. The current equivalent of a changing electric flux ✓
C. Current produced by moving charges in a conductor
D. Current that causes displacement of electrons

Answer: B. The current equivalent of a changing electric flux
Displacement current is defined as the current equivalent of a changing electric flux through a medium, introduced by Maxwell to explain electromagnetic induction.

Which equation introduced the concept of displacement current?

A. Gauss's law
B. Faraday's law
C. Ampère-Maxwell law ✓
D. Coulomb's law

Answer: C. Ampère-Maxwell law
Maxwell modified Ampère's law by adding the displacement current term, creating the Ampère-Maxwell law which is fundamental to electromagnetic wave theory.

Radio waves are used for communication because they:

A. Have very high frequency
B. Have long wavelengths and can penetrate obstacles ✓
C. Are strongly absorbed by the atmosphere
D. Travel faster than other electromagnetic waves

Answer: B. Have long wavelengths and can penetrate obstacles
Radio waves have long wavelengths and low frequencies, allowing them to diffract around obstacles and penetrate buildings, making them ideal for communication.

The relationship between the amplitudes of electric field (E₀) and magnetic field (B₀) in an electromagnetic wave is:

A. E₀ = B₀
B. E₀ = cB₀ ✓
C. B₀ = cE₀
D. E₀ + B₀ = c

Answer: B. E₀ = cB₀
The amplitude of the electric field and magnetic field in an electromagnetic wave are related by E₀ = cB₀, where c is the speed of light.

The concept of displacement current was introduced because:

A. Ampère's law was incomplete for time-varying electric fields ✓
B. Moving charges always produce currents
C. Magnetic fields cannot change with time
D. Electric fields in conductors are always constant

Answer: A. Ampère's law was incomplete for time-varying electric fields
Displacement current was introduced by Maxwell to modify Ampère's law, making it valid for time-varying electric fields and completing the set of equations that predict electromagnetic waves.