Objective Type Question Answers On Class 12 Physics Chapter 8 Electromagnetic Waves

1 A plane electromagnetic wave is incident on a material surface. The wave delivers momentum p and energy E. Then

A p ≠ 0, E ≠ 0

B p = 0, E = 0

C p = 0, E ≠ 0

D p ≠ 0, E = 0

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Answer:p ≠ 0, E = 0

2 The electric and magnetic field of an electromagnetic wave are:

A in opposite phase and perpendicular to each other

B in opposite phase and parallel to each other

C in phase and perpendicular to each other

D in phase and parallel to each other

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Answer:in phase and perpendicular to each other

3 The electromagnetic wave used to treat muscular pain is:

A VHF radiowaves

B X-rays

C Ultraviolet rays

D Infrared radiations

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Answer:Infrared radiations

4 A beam of light travelling along x-axis is described by the magnetic field B_z = 5 X 10^-7T sinω(t – x/c) If a beam of alpha particle moves in this filed along y – axis with a speed of 3 X 10⁷ m/s, then the maximum electric and magnetic forces experienced by it will be:

A 4.80 X 10^-10N and 4.8 X 10^-12N respectively.

B 4.80 X 10^-17N and 4.8 X 10^-18N respectively.

C 2.80 X 10^-5N and 2.1 X 10^-7N respectively.

D 1.5 X 10^-5N and 4.1 X 10^-7N respectively.

View Answer

Answer:4.80 X 10^-17N and 4.8 X 10^-18N respectively.

5 An electromagnetic wave propagating along north has its electric field vector upwards. Its magnetic field vector point towards

A north

B east

C west

D downwards

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Answer:east

6 According to Maxwell’s hypothesis, a changing electric field gives rise to

A an e.m.f

B electric displacement current

C magnetic field

D pressure gradient

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Answer:magnetic field

7 Which of the following has/have zero average value in a plane electromagnetic wave?

A Both magnetic and electric field

B Electric field only

C Magnetic energy

D Electric energy

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Answer:Both magnetic and electric field

8 Select the wrong statement. EM waves

A are transverse in nature.

B travel in free space at a speed of light.

C are produced by accelerating charges.

D travel in all media with same speed.

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Answer:travel in all media with same speed.

9 An electron oscillating with a frequency of 3 × 10⁶ Hz, would generate

A X-rays

B ultraviolet rays

C radio waves

D microwaves

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Answer:radio waves

10 Displacement current goes through the gap between the plates of a capacitor when the charge on the capacitor

A is changing with time

B decreases

C does not change

D decreases to zero

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Answer:is changing with time

11 If a variable frequency ac source connected to a capacitor then with decrease in frequency, the displacement current will

A increase

B decrease

C remain constant

D first decrease then increase

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Answer:decrease

12 The current in the electric circuit which arises due to flow of electrons in the connecting wires of the circuit in a defined closed path is called

A alternating current

B direct current

C conduction current

D displacement current

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