CBSE Board Exam 2020: Important MCQs (with Answers) for Class 12 Physics - Chapter 8 - Electromagnetic Waves; Also useful for JEE Main, UPSEE, WBJEE & Other Engineering Entrance Exams

Check important MCQs (with Answers) for CBSE Class 12 Physics Board Exam 2020 (Chapter 8 - Electromagnetic Waves). Students preparing for CBSE Class 12th Physics Board Exam usually ask about important MCQs (Multiple Choice Questions) & in this article, we are going to provide important questions, based on Chapter 8 (Electromagnetic Waves) of Class 12 Physics NCERT textbook. Here you will also get links to access some important articles for the preparation of CBSE 12th board exams 2020.

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CBSE Board Exam 2020: Important MCQs (with Answers) for Class 12 Physics, Chapter 8 - Electromagnetic Waves

(a) 1 X 10^-8 T

(b) 2.1 X 10^-8T

(c) 2.1 X 10^-4T

(d) 6 X 10^-4T

Sol: (b)

2. 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.

Sol: (b)

3. The electromagnetic wave used to treat muscular pain is:

(a) VHF radiowaves

(b) X-rays

(c) Ultraviolet rays

(d) Infrared radiations

Sol: (d)

Infrared radiations are used to treat muscular pain.

4. The correct formula for the velocity of light in a material medium of relative permittivity ε_r and relative magnetic permeability μ_r

(d) None of these

Sol: (b)

Sol: (c)

Sol:  (d)

7. 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

Sol:  (c)

In electromagnetic wave, electric and magnetic field are in phase and perpendicular to each other and also perpendicular to the direction of propagation of the electromagnetic wave.

8. The velocity of electromagnetic radiation in a medium of permittivity ϵ₀ and permeability μ₀ is given by

Sol: (c)

9. If μ₀ be the permeability and k₀, the dielectric constant of a medium, its refractive index is given by

Sol: (c)

10. 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

Sol: (d)

When plane electromagnetic wave is incident on a material surface, the wave delivers some momentum and energy to the surface and hence p ≠ 0 and E ≠ 0.