# NEET

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

## Biology

Electromagnetic Waves

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Q 1. An electromagnetic wave in vacuum has the electric and magnetic field {tex} \vec { E } {/tex} and {tex} \vec { B } {/tex} , which are always perpendicular to each other. The direction of polarization is given by {tex} \vec { X } {/tex} and that of wave propagation by {tex} \vec { k } . {/tex} Then

A

{tex} \overline { X } \| \vec { B } {/tex} and {tex} \vec { k } \| \vec { B } \times \vec { E } {/tex}

{tex} \overline { X } \| \overline { E } {/tex} and {tex} \vec { k } \| \vec { E } \times \vec { B } {/tex}

C

{tex} \vec { X } \| \vec { B } {/tex} and {tex} \vec { k } \| \vec { E } \times \vec { B } {/tex}

D

{tex} \vec { X } \| \vec { E } {/tex} and {tex} \vec { k } \| \vec { B } \times \vec { E } {/tex}

##### Explanation

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Q 2. The rms value of the electric field of the light coming from the Sun is 720 {tex} \mathrm { N } / \mathrm { C } {/tex} . The average total energy density of the electromagnetic wave is

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

B

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

C

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

D

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

##### Explanation

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Q 3. An electromagnetic wave with frequency {tex} \omega {/tex} and wavelength {tex} \lambda {/tex} travels in the {tex} + y {/tex} direction. Its magnetic field is along {tex} + x - {/tex}axis. The vector equation for the associated electric field (of {tex} \left. \text { amplitude } E _ { 0 } \right) {/tex} is

A

{tex} \vec { E } = - E _ { 0 } \cos \left( \omega t + \frac { 2 \pi } { \lambda } y \right) \hat { x } {/tex}

B

{tex} \vec { E } = E _ { 0 } \cos \left( \omega t - \frac { 2 \pi } { \lambda } y \right) \hat { x } {/tex}

{tex} \vec { E } = E _ { 0 } \cos \left( \omega t - \frac { 2 \pi } { \lambda } y \right) \hat { z } {/tex}

D

{tex} \vec { E } = - E _ { 0 } \cos \left( \omega t + \frac { 2 \pi } { \lambda } y \right) \hat { z } {/tex}

##### Explanation

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Q 4. An electromagnetic wave of frequency {tex} v = 3.0 \mathrm { MHz } {/tex} passes from vacuum into a dielectric medium with permittivity {tex} \mathrm { E } = 4.0 . {/tex} Then

wavelength is halved and frequency remains unchanged

B

wavelength is doubled and frequency becomes half

C

wavelength is doubled and the frequency remains unchanged

D

wavelength and frequency both remain unchanged.

##### Explanation

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Q 5. If {tex} v _ { s } , v _ { x } {/tex} and {tex} v _ { m } {/tex} are the speed of soft gamma rays, X-rays and microwaves respectively in vacuum, then

A

{tex} \mathrm{v} _ { s } > \mathrm{v} _ { x } > \mathrm{v} _ { m } {/tex}

B

{tex} \mathrm { v } _ { \mathrm { s } } < \mathrm { v } _ { \mathrm { x } } < \mathrm { v } _ { \mathrm { m } } {/tex}

C

{tex} \mathrm { v } _ { \mathrm { s } } > \mathrm { v } _ { \mathrm { x } } < \mathrm { v } _ { \mathrm { m } } {/tex}

{tex} \mathrm{v} _ { s } = \mathrm{v} _ { x } = \mathrm{v} _ { m } {/tex}

##### Explanation

Increasing order of frequencies of spectrum is given by,
Radio wave < micro wave < infrared wave < visible rays < ultraviolet rays < x-rays < gamma rays < cosmic rays
Order of wavelengths of spectrum is given by,
Radio wave > micro wave > infrared wave > visible rays > ultraviolet rays > x-rays > gamma rays > cosmic rays
Because all radiations are component of electromagnetic wave and speed of electromagnetic wave is m/s in vaccum.Hence,
{tex}V_g = V_x = V_m = \frac{m}{s}{/tex}

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Q 6. Photons of an electromagnetic radiation has an energy 11 keV each. To which region of electromagnetic spectrum does it belong?

X-ray region

B

Ultra violet region

C

Infrared region

D

Visible region

##### Explanation

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Q 7. Intensity of electromagnetic wave will be

A

{tex} \mathrm { I } = \mathrm { c } \mu _ { 0 } \mathrm { B } _ { 0 } ^ { 2 } / 2 {/tex}

{tex} \mathrm { I } = \mathrm { c } \varepsilon _ { 0 } \mathrm { E } _ { 0 } ^ { 2 } / 2 {/tex}

C

{tex} \mathrm { I } = \mathrm { B } _ { 0 } ^ { 2 } / \mathrm { c } \mu _ { 0 } {/tex}

D

{tex} \mathrm { I } = \mathrm { E } _ { 0 } ^ { 2 } / 2 \mathrm { c } \varepsilon _ { 0 } {/tex}

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Q 8. Which radiation in sunlight, causes heating effect?

A

Ultraviolet

Infrared

C

Visible light

D

All of these

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Q 9. Electromagnetic radiation of highest frequency is

A

B

C

{tex} \gamma {/tex} - rays

##### Explanation

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Q 10. A point source of electromagnetic radiation has an average power output of 1500W. The maximum value of electric field at a distance of 3m from this sources in Vm-1 is

A

500

100

C

{tex} \frac { 500 } { 3 } {/tex}

D

{tex} \frac { 250 } { 3 } {/tex}

##### Explanation

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Q 11. Which of the following statement is false for the properties of electromagnetic waves?

A

Both electric and magnetic field vectors attain the maxima and minima at the same place and same time.

B

The energy in electromagnetic wave is divided equally between electric and magnetic vectors

Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave

D

These waves do not require any material medium for propagation.

##### Explanation

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Q 12. The wave impendance of free space is

A

zero

1883{tex} \Omega {/tex}

C

18.83{tex} \Omega {/tex}

D

188.3{tex} \Omega {/tex}