If ${{\rm{\varepsilon }}_0}{\rm{\;and\;}}{{\rm{\mu }}_0}$ are the electric permittivity and magnetic permeability of free space and ${\rm{\varepsilon \;and\;\mu }}$ are the corresponding quantities in the medium, the index of refraction of the medium in terms of above parameter is

${\left( {\frac{{{\rm{\varepsilon \mu }}}}{{{{\rm{\varepsilon }}_0}{{\rm{\mu }}_0}}}\begin{array}{*{20}{c}} {\rm{\;}}\\ {\rm{\;}} \end{array}} \right)^{1/2}}$

$\frac{{{\rm{\varepsilon \mu }}}}{{{{\rm{\varepsilon }}_0}{{\rm{\mu }}_0}}}$

$\left( {\frac{{{{\rm{\varepsilon }}_0}{{\rm{\mu }}_0}}}{{{\rm{\varepsilon \mu }}}}} \right)$

${\left( {\frac{{{{\rm{\varepsilon }}_0}{{\rm{\mu }}_0}}}{{{\rm{\varepsilon \mu }}}}} \right)^{1/2}}{\rm{\;}}$

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JEE • PHYSICS • ELECTROMAGNETIC WAVES

Electromagnetic waves practice · Mixed difficulty

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These sets use single-correct-answer MCQs. They do not cover every JEE Main or JEE Advanced question format and are not full-length mock papers.

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151 Medium

151 of 250

Understanding +4 | -1

Statement I: Ultra violet radiations being higher frequency waves are dangerous to human beings.

Statement II: Ultraviolet radiations are absorbed by the atmosphere

View answer and explanation

Correct option: B

Statement I is true; statement II is false

Option B (Statement I is true; statement II is false) is correct because UV radiation is high frequency and harmful, but it's mostly absorbed by the ozone layer, not the entire atmosphere.

152 Medium

152 of 250

Understanding +4 | -1

Assertion: Dipole oscillations produce electromagnetic waves

Reason: Accelerated charge produces electromagnetic waves

View answer and explanation

Correct option: A

Both Assertion and reason are true and the reason is correct explanation of the Assertion.

Option A is correct because dipole oscillations involve accelerating charges, which produce electromagnetic waves, making the reason a correct explanation of the assertion.

153 Medium

153 of 250

Understanding +4 | -1

A plane electromagnetic wave is traveling in vacuum in X-direction. The plane in which
magnetic field propagates is

View answer and explanation

Correct option: A

X-Y

Option A (X-Y) is correct because the magnetic field propagates in a plane perpendicular to the direction of propagation (X-direction) and the electric field.

154 Medium

154 of 250

Understanding +4 | -1

Statement I: Electromagnetic waves exert pressure, called radiation pressure.

Statement II: Electromagnetic waves carry energy.

View answer and explanation

Correct option: A

Statement I and statement II are true

Option A is correct because electromagnetic waves do exert radiation pressure and they carry energy, both of which are fundamental properties of these waves.

155 Medium

155 of 250

Remembering +4 | -1

In which one of the following regions of the electromagnetic spectrum will the vibrational motion of molecules give rise to absorption

View answer and explanation

Correct option: B

Microwaves

Option B (Microwaves) is correct because vibrational motions of molecules give rise to absorption in the microwave region of the electromagnetic spectrum.

156 Medium

156 of 250

Application +4 | -1

An electromagnetic wave with frequency

\omega

and wavelength

\lambda

travels in the

+y

direction. Its magnetic field is along

+x-

axis. The vector equation for the associated electric field (of amplitude

E_0

) is

View answer and explanation

Correct option: C

\vec{E}=E_0 \cos \left(\omega t-\frac{2 \pi}{\lambda} y\right) \hat{z}

Option C (

\vec{E}=E_0 \cos \left(\omega t-\frac{2 \pi}{\lambda} y\right) \hat{z}

) is correct because it represents an electromagnetic wave traveling in the +y direction with the magnetic field along the +x axis, thus the electric field must be along the +z axis and in phase.

157 Medium

157 of 250

Remembering +4 | -1

Which scientist experimentally proved the existence of electromagnetic waves

View answer and explanation

Correct option: D

Hertz

Option D (Hertz) is correct because Hertz experimentally proved the existence of electromagnetic waves.

158 Medium

158 of 250

Understanding +4 | -1

{\mathrm{\varepsilon }_0}\mathrm{\;and\;}{\mathrm{\mu }_0}

are the electric permittivity and magnetic permeability of free space and

\mathrm{\varepsilon \;and\;\mu }

are the corresponding quantities in the medium, the index of refraction of the medium in terms of above parameter is

View answer and explanation

Correct option: B

{\left( {\frac{{\mathrm{\varepsilon \mu }}}{{{\mathrm{\varepsilon }_0}{\mathrm{\mu }_0}}}\begin{array}{cccccccccccccccccccc} \mathrm{\;}\\ \mathrm{\;} \end{array}} \right)^{1/2}}

Option B (

{\left( {\frac{{\mathrm{\varepsilon \mu }}}{{{\mathrm{\varepsilon }_0}{\mathrm{\mu }_0}}}\begin{array}{cccccccccccccccccccc}\mathrm{\;}\\mathrm{\;}\end{array}} \right)^{1/2}}

) is correct because the refractive index is the ratio of the speed of light in vacuum to the speed of light in the medium, which can be expressed in terms of permittivity and permeability.

159 Easy

159 of 250

Analyzing +4 | -1

A proton moving with a constant velocity passes through a region of space without any change in its velocity. If

\vec{E}

and

\vec{B}

represent the electric and magnetic fields respectively, then the region of space may have:

(A)

E=0, B=0

(B)

E=0, B \neq 0

(C)

E \neq 0, B=0

(D)

E \neq 0, B \neq 0

Choose the most appropriate answer from the options given below:

View answer and explanation

Correct option: C

(A), (B) and (D) only

Option C is correct. A proton can pass through a region with no change in velocity if E=0, B=0; E=0, B� 0 (if velocity is parallel to B); or E� 0, B� 0 (if electric and magnetic forces cancel each other).

160 Medium

160 of 250

Understanding +4 | -1

In free space, the energy of electromagnetic wave in electric field is

{U_E}

and in magnetic field is

{U_B}

. Then

View answer and explanation

Correct option: A

{U_E} = {U_B}

Option A (

{U_E} = {U_B}

) is correct because the energy is equally distributed between the electric and magnetic fields in an electromagnetic wave.

161 Medium

161 of 250

Understanding +4 | -1

The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to :

View answer and explanation

Correct option: B

reciprocal of speed of light in vacuum

Option B (reciprocal of speed of light in vacuum) is correct because the ratio of the magnetic field amplitude to the electric field amplitude in an EM wave is 1/c.

162 Medium

162 of 250

Understanding +4 | -1

During the propagation of electromagnetic waves in a medium

View answer and explanation

Correct option: C

electric energy density is equal to the magnetic energy density

Option C (electric energy density is equal to the magnetic energy density) is correct because in electromagnetic waves, the energy is equally divided between the electric and magnetic fields.

163 Medium

163 of 250

Remembering +4 | -1

Choose the correct option relating wavelengths of different parts of electromagnetic wave spectrum

View answer and explanation

Correct option: C

{\lambda _{\mathrm{radio waves}}} > {\lambda _{\mathrm{micro waves}}} > {\lambda _{\mathrm{visible}}} > {\lambda _{\mathrm{X - rays}}}

Option C (

{\lambda _{\mathrm{radio waves}}} > {\lambda _{\mathrm{micro waves}}} > {\lambda _{\mathrm{visible}}} > {\lambda _{\mathrm{X - rays}}}

) is correct because it accurately represents the order of wavelengths in the electromagnetic spectrum, from longest to shortest.

164 Medium

164 of 250

Remembering +4 | -1

The pressure exerted by an electromagnetic wave of intensity I

\left(\mathrm{Wm}^{-2}\right)

on a non-reflecting surface is (

C

is the velocity of light)

View answer and explanation

Correct option: C

I/c

Option C (

I/c

) is correct because the pressure exerted by an electromagnetic wave on a non-reflecting surface is given by the intensity divided by the speed of light.

165 Medium

165 of 250

Understanding +4 | -1

Displacement current is a source of

View answer and explanation

Correct option: D

time varying magnetic field

Option D (time varying magnetic field) is correct because displacement current, which arises from a time-varying electric field, acts as a source of a time-varying magnetic field, similar to conduction current.

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UNITS & MEASUREMENTS 633 MCQs WAVES 566 MCQs THERMAL PROPERTIES OF MATTER 564 MCQs WORK-ENERGY-POWER 553 MCQs MOTION IN PLANE 530 MCQs OSCILLATIONS 498 MCQs

166 Hard

166 of 250

Remembering +4 | -1

Electromagnetic energy is radiated by:

(a) Stationary charge

(b) A charge in uniform motion

(c) An accelerated charge only

(d) An accelerated charge and a charge in uniform motion

Choose the correct statement.

View answer and explanation

Correct option: C

Option C ((c) only) is correct because only an accelerated charge radiates electromagnetic energy.

167 Medium

167 of 250

Understanding +4 | -1

Which one of the following rays (or wave) has
maximum speed in air?

View answer and explanation

Correct option: D

Heat radiations

Option D is correct because heat radiations, being electromagnetic waves, travel at the speed of light in air, which is the maximum speed among the given options.

168 Medium

168 of 250

Application +4 | -1

The electric field of an electromagnetic wave is given by

E=100 \sin \omega\left(t-\frac{x}{v}\right) N / C.

Find the energy contained in a hypothetical space of volume

100 \mathrm{~cm}^3

(Given

\left.\epsilon_0=9 \times 10^{-12} C^2 N^{-1} m^{-2}\right)

View answer and explanation

Correct option: C

2.25 \times 10^{-12} \mathrm{~J}

Option C (

2.25 \times 10^{-12} \mathrm{~J}

) is correct because the energy density of an electromagnetic wave is proportional to the square of the electric field, and the energy is the energy density times the volume.

169 Medium

169 of 250

Remembering +4 | -1

The range of wavelengths for visible light is

View answer and explanation

Correct option: C

4000 \mathop {\text{A}}\limits^{\text{o}}

8000 \mathop {\text{A}}\limits^{\text{o}}

Option C (

4000 \mathop {\text{A}}\limits^{\text{o}}

8000 \mathop {\text{A}}\limits^{\text{o}}

) is correct because the visible light spectrum ranges approximately from 400 nm to 800 nm, which is 4000 to 8000 Angstroms.

170 Medium

170 of 250

Understanding +4 | -1

Which of the following Maxwell's equation is valid for time varying conditions but not valid for static conditions:

View answer and explanation

Correct option: D

\oint \vec{E} \cdot \overrightarrow{d l}=-\frac{\partial \phi_{B}}{\partial t}

Option D (

\oint \vec{{E}} \cdot \overrightarrow{{dl}}=-\frac{{\partial \phi_{{B}}}}{{\partial t}}

) is correct because this is Faraday's law of induction, which is only valid for time-varying magnetic fields.

171 Medium

171 of 250

Understanding +4 | -1

Assertion: Radar is used to detect an aeroplane in the sky

Reason: Radar works on the principle of reflection of waves.

View answer and explanation

Correct option: A

If both assertion and reason are true and the reason is the correct explanation of the assertion.

Option A is correct because radar uses the reflection of radio waves to detect objects like airplanes.

172 Medium

172 of 250

Understanding +4 | -1

Assertion: In electromagnetic waves electric field and magnetic field lines are perpendicular to each other.

Reason: E and B are self - sustaining

View answer and explanation

Correct option: B

If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion

The correct answer is B (If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion) because both statements are true, but the self-sustaining nature of E and B doesn't directly explain their perpendicularity.

173 Medium

173 of 250

Remembering +4 | -1

Which of the following is correct?

View answer and explanation

Correct option: D

All of these

Option D (All of these) is correct because Maxwell's equations describe that a time-varying magnetic field produces an electric field, a time-varying electric field produces a magnetic field, and E = Bc relates the magnitudes of the electric and magnetic fields in an electromagnetic wave.

174 Medium

174 of 250

Understanding +4 | -1

Statement I: If earth did not have atmosphere, its average surface temperature would be lower than the present average surface temperature

Statement II: Greehouse effect would be absent if earth did not have atmosphere

View answer and explanation

Correct option: A

Statement I and statement II are true

Option A is correct because the absence of an atmosphere would result in a lower average surface temperature due to the lack of the greenhouse effect.

175 Medium

175 of 250

Application +4 | -1

A plane electromagnetic wave of wave intensity

6 {Wm}^{-2}

strikes a small mirror of area

30 {~cm}^2

, held perpendicular to the approaching wave. The the mirror each second will be

View answer and explanation

Correct option: A

1.2 \times 10^{-10}

Option A (

1.2 \times 10^{-10}

) is correct because the momentum transferred is calculated using the formula p = 2IA/c, where I is the intensity, A is the area, and c is the speed of light.

176 Medium

176 of 250

Analyzing +4 | -1

\mathrm{E}

and

\mathrm{B}

denote electric and magnetic fields respectively, which of the following is dimensionless?

View answer and explanation

Correct option: A

\sqrt{\mu_0 \varepsilon_0} \frac{\mathrm{E}}{\mathrm{B}}

Option A is correct because the expression

\sqrt{μ_0 ε_0}

\frac{\mathrm{E}}{\mathrm{B}}

is dimensionless, as

\sqrt{μ_0 ε_0}

is the inverse of the speed of light and

\frac{\mathrm{E}}{\mathrm{B}}

is the speed of light.

177 Easy

177 of 250

Application +4 | -1

An electromagnetic wave has electric field given by

\vec{E}=(9.6 \hat{j}) \sin \left[2 \pi\left\{30 \times 10^6 t-\frac{1}{10} x\right\}\right], x

and

t

are in SI units. The maximum magnetic field is

View answer and explanation

Correct option: A

3.2 \times 10^{-9}

Option A (

3.2 \times 10^{-9}

) is incorrect. The correct answer is

3.2 \times 10^{-8}

because the maximum magnetic field is found using

B = \frac{E}{c}

178 Medium

178 of 250

Remembering +4 | -1

The intensity of electromagnetic wave is equal to (symbols have their usual meanings)

View answer and explanation

Correct option: A

\varepsilon_0 E_{{rms}} B_{{rms}} C^2

Option B (

\varepsilon_0 E^2

rms) is incorrect. The correct formula is

I = c \epsilon_0 E_{rms}^2 = c \frac{B_{rms}^2}{ \mu_0} = c \epsilon_0 E_{rms}B_{rms}

179 Medium

179 of 250

Understanding +4 | -1

If the total electromagnetic energy falling on a surface is

U

, then the total momentum delivered (for complete absorption) is

View answer and explanation

Correct option: A

\frac{U}{c}

Option A (

\frac{U}{c}

) is correct because the momentum delivered for complete absorption is the energy divided by the speed of light.

180 Medium

180 of 250

Application +4 | -1

The amplitude of the sinusoidally oscillating electric field of plane wave is

60\,\,\frac{V}{m}

. Then the amplitude of the magnetic field is

View answer and explanation

Correct option: D

2 \times {10^{ - 7}}T

Option D (

2 \times {10^{ - 7}}T

) is correct because it is calculated using the relationship between the electric field amplitude, magnetic field amplitude, and the speed of light.

Revision notes and key takeaways

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