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JEE Main

Explore popular questions from Electromagnetic Waves for JEE Main. This collection covers Electromagnetic Waves previous year JEE Main questions hand picked by experienced teachers.

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Electromagnetic Waves

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Q 1. If {tex} E {/tex} and {tex} B {/tex} are the electric and magnetic field vectors of electromagnetic waves then the direction of propagation of electromagnetic wave is along the direction of

A

{tex} \vec { E } {/tex}

B

{tex} \vec { B } {/tex}

{tex} \vec { E } \times \vec { B } {/tex}

D

None of these

Explanation

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Q 2. The wave function (in S.I. units) for an electromagnetic wave is given as{tex} \Psi ( x , t ) = 10 ^ { 3 } \sin \pi \left( 3 \times 10 ^ { 6 } x - 9 - 10 ^ { 14 } t \right) {/tex}.The speed of the wave as

A

{tex} 9 \times 10 ^ { 14 } \mathrm { m } / \mathrm { s } {/tex}

{tex} 3 \times 10 ^ { 8 } \mathrm { m } / \mathrm { s } {/tex}

C

{tex} 3 \times 10 ^ { 16 } \mathrm { m } / \mathrm { s } {/tex}

D

{tex} 3 \times 10 ^ { 7 } \mathrm { m } / \mathrm { s } {/tex}

Explanation

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Q 3. Out of four Maxwell's equations, which one shows non-existence of monopoles?

A

(i) and (iv)

(ii) Only

C

(iii) Only

D

(i) Only

Explanation

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Q 4. In an electromagnetic wave the average energy density is associated with

A

electric field only.

B

magnetic field only

equally with electric and magnetic fields.

D

average energy density is zero

Explanation

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Q 5. In an electromagnetic wave the average energy density associated with magnetic field will be

A

{tex} \frac { 1 } { 2 } L I ^ { 2 } {/tex}

{tex} \frac { B ^ { 2 } } { 2 \mu _ { 0 } } {/tex}

C

{tex} \frac { 1 } { 2 } \mu _ { 0 } B ^ { 2 } {/tex}

D

{tex} \frac { 1 } { 2 } \frac { q } { B ^ { 2 } } {/tex}

Explanation

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Q 6. In the above problem, the energy density associated with the electric field will be

A

{tex} \frac { 1 } { 2 } C V ^ { 2 } {/tex}

B

{tex} \frac { 1 } { 2 } \frac { q ^ { 2 } } { C } {/tex}

C

{tex} \frac { 1 } { 2 } \frac { \varepsilon ^ { 2 } } { E } {/tex}

{tex} \frac { 1 } { 2 } \varepsilon _ { 0 } E ^ { 2 } {/tex}

Explanation

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Q 7. If there were no atmosphere, the average temperature on earth surface would be

Lower

B

Higher

C

Same

D

{tex} 0 ^ { \circ } \mathrm { C } {/tex}

Explanation

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Q 8. The displacement current flows in the dielectric of a capacitor

A

becomes zero.

B

has assumed a constant value.

is increasing with time.

D

is decreasing with time.

Explanation

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Q 9. Select wrong statement from the following Electromagnetic waves

A

are transverse.

travel with same speed in all media.

C

travel with the speed of light.

D

are produced by acceleration charge.

Explanation

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Q 10. The waves related to telecommunication are

A

Infra red

B

Visible light

Microwaves

D

Ultraviolet rays

Explanation

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Q 11. Electromagnetic waves do not transport

Energy

B

Charge

C

Momentum

D

Information

Explanation

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Q 12. The nature of electromagnetic wave is

A

Longitudinal

B

Longitudinal stationary

Transverse

D

Transverse stationary

Explanation

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Q 13. Greenhouse effect keeps the earth surface

A

Cold at night

B

Dusty and cold

Warm at night

D

Moist

Explanation

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Q 14. A parallel plate capacitor consists of two circular plates each of radius 12{tex} \mathrm { cm } {/tex} and separated by 5.0{tex} \mathrm { mm } {/tex} . The capacitor is being charged by an external source.The charging is being charged and is equal to 0.15{tex} \mathrm { A } {/tex} . The rate of change of potential difference between the plates will be

A

{tex} 8.173 \times 10 ^ { 7 } \mathrm { V } / \mathrm { s } {/tex}

B

{tex} 7.817 \times 10 ^ { 8 } \mathrm { V } / \mathrm { s } {/tex}

{tex} 1.873 \times 10 ^ { 9 } \mathrm { V } / \mathrm { s } {/tex}

D

{tex} 3.781 \times 10 ^ { 10 } \mathrm { V } / \mathrm { s } {/tex}

Explanation

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Q 15. In the above problem, the displacement current is

A

15{tex} \mathrm { A } {/tex}

B

1.5 {tex} \mathrm { A } {/tex}

0.15 {tex} \mathrm { A } {/tex}

D

0.015 {tex} \mathrm { A } {/tex}

Explanation

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Q 16. Infrared radiation is detected by

A

spectrometer

pyrometer

C

nanometer

D

photometer

Explanation


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Q 17. Which of the following are not electromagnetic waves?

A

cosmic rays

B

gamma rays

{tex} \beta {/tex} -rays

D

X-rays.

Explanation

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Q 18. The rms value of the electric field of the light coming from the sun is {tex} 720 \mathrm { N } / \mathrm { C } {/tex}. The average total energy density of the electromagnetic wave is

A

{tex} 3.3 \times 10 ^ { - 3 } \mathrm { J } / \mathrm { m } ^ { 3 } {/tex}

{tex} 4.58 \times 10 ^ { - 6 } \mathrm { J } / \mathrm { m } ^ { 3 } {/tex}

C

{tex} 6.37 \times 10 ^ { - 9 } \mathrm { J } / \mathrm { m } ^ { 3 } {/tex}

D

{tex} 81.35 \times 10 ^ { - 12 } \mathrm { J } / \mathrm { m } ^ { 3 } {/tex}

Explanation



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Q 19. An electromagnetic wave of frequency {tex}\upsilon = 3.0 \mathrm { MHz } {/tex} passes from vacuum into a dielectric medium with permitivity {tex} \varepsilon = 4.0 . {/tex} Then

A

wavelength is doubled and the frequency remains unchanged

B

wavelength is doubled and frequency becomes half

wavelength is halved and frequency remains unchanged

D

wavelength and frequency both remain unchanged.

Explanation



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Q 20. Consider telecommunication through optical fibres Which of the following statements is not true?

A

Optical fibres can be of graded refractive index.

Optical fibres are subject to electromagnetic interference from outside.

C

Optical fibres have extremely low transmission loss.

D

Optical fibres may have homogeneous core with a suitable cladding.

Explanation


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Q 21. Electromagnetic waves are transverse in nature is evident by

polarization

B

interference

C

reflection

D

diffraction

Explanation


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Q 22. In which part of earth's atmosphere is the ozone layer present?

A

Troposphere

Stratosphere

C

Ionosphere

D

Mesosphere

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Q 23. Kenneley's Heaviside layer lies between

A

50{tex} \mathrm { km } {/tex} to 80{tex} \mathrm { km } {/tex}

B

80{tex} \mathrm { km } {/tex} to 400{tex} \mathrm { km } {/tex}

beyond 110{tex} \mathrm { km } {/tex}

D

beyond 250{tex} \mathrm { km } {/tex}

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Q 24. The ozone layer in earth's atmosphere is crucial for human survival because it

A

has ions.

B

reflects radio signals.

reflects ultraviolet ray.

D

reflects infra red rays.

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Q 25. The frequency from {tex} 3 \times 10 ^ { 9 } \mathrm { Hz } {/tex} to {tex} 3 \times 10 ^ { 10 } \mathrm { Hz } {/tex}

A

low frequency band

Super high frequency band

C

Ultra high frequency band

D

High frequency band