Electromagnetic Waves NEET PYQs | Practice Important Physics Questions

Q 1 :
The electric field in a plane electromagnetic wave is given by $E_{z} = 60 \cos (5 x + 1.5 \times 10^{9} t) V/m .$

Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field) [2025]

$B_{z} = 60 \cos (5 x + 1.5 \times 10^{9} t)$ $T$
$B_{y} = 60 \sin (5 x + 1.5 \times 10^{9} t)$ $T$
$B_{y} = 2 \times 10^{- 7} \cos (5 x + 1.5 \times 10^{9} t)$ $T$
$B_{x} = 2 \times 10^{- 7} \cos (5 x + 1.5 \times 10^{9} t)$ $T$

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(3)

Given, $E_{z} = 60 \cos (5 x + 1.5 \times 10^{9} t)$ $V/m$

As, $B_{0} = \frac{E_{0}}{c} \Rightarrow B_{0} = \frac{60}{3 \times 10^{8}} = 2 \times 10^{- 7}$ $T$

Since, In an electromagnetic wave, the direction of wave propagation is along

$\vec{E} \times \vec{B}$ thus magnetic field will be along $y$ -direction.

$∴$ $B_{y} = 2 \times 10^{- 7} \cos (5 x + 1.5 \times 10^{9} t) J$

Q 2 :
If the ratio of relative permeability and relative permittivity of a uniform medium is 1 : 4. The ratio of the magnitudes of electric field intensity $(E)$ to the magnetic field intensity $(H)$ of an EM wave propagating in that medium is

$(Given that \sqrt{\frac{μ_{0}}{ε_{0}}} = 120 π)$ [2024]

$30 π : 1$
$1 : 120 π$
$60 π : 1$
$120 π : 1$

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(3)

Given, $\frac{μ_{r}}{ε_{r}} = \frac{1}{4}$

From $c = \frac{1}{\sqrt{μ ε}} and c = \frac{E}{B}$

$\frac{1}{\sqrt{μ ε}} = \frac{E}{B}$ ...(i) and $B = μ H$ ...(ii)

Putting (ii) in equation (i), we get

$\frac{E}{μ H} = \frac{1}{\sqrt{μ ε}}$

$∴$ $\frac{E}{H} = \frac{μ}{\sqrt{μ ε}} = \sqrt{\frac{μ}{ε}} = \sqrt{\frac{μ_{0} μ_{r}}{ε_{0} ε_{r}}}$

$= \sqrt{\frac{μ_{0}}{ε}} \sqrt{\frac{μ_{r}}{ε_{r}}} = 120 π \times \sqrt{\frac{1}{4}} = \frac{120 π}{2} = 60 π$

$∴$ $E : H = 60 π : 1$

Q 3 :
The property which is not of an electromagnetic wave travelling in free space is that [2024]

they are transverse in nature.
the energy density in electric field is equal to energy density in magnetic field.
they travel with a speed equal to $\frac{1}{\sqrt{μ_{0} ε_{0}}} .$
they originate from charges moving with uniform speed.

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(4)

When charge is accelerated then, time-varying electric and magnetic fields are produced, thus electromagnetic wave is produced by accelerated charge.

Q 4 :
In a plane electromagnetic wave travelling in free space, the electric field component oscillates sinusoidally at a frequency of $2.0 \times 10^{10}$ Hz and amplitude 48 ${Vm}^{- 1}$ . Then the amplitude of oscillating magnetic field is
(Speed of light in free space = $3 \times 10^{8}$ $m$ $s^{- 1}$ ) [2023]

$1.6 \times 10^{- 7} T$
$1.6 \times 10^{- 6} T$
$1.6 \times 10^{- 9} T$
$1.6 \times 10^{- 8} T$

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(1)

Frequency of E.M. wave, $υ = 2.0 \times 10^{10} Hz$

Electric field amplitude, $E_{0} = 48$ $V$ $m^{- 1}$

Speed of light, $c = 3 \times 10^{8} m/s$

Magnetic field strength is given as:

$B_{0} = \frac{E_{0}}{c} = \frac{48}{3 \times 10^{8}} = 1.6 \times 10^{- 7} T$

Q 5 :
When light propagates through a material medium of relative permittivity $ε_{r}$ and relative permeability $μ_{r}$ , the velocity of light, $v$ is given by (c - velocity of light in vacuum) [2022]

$v = c$
$v = \sqrt{\frac{μ_{r}}{ε_{r}}}$
$v = \sqrt{\frac{ε_{r}}{μ_{r}}}$
$v = \frac{c}{\sqrt{ε_{r} μ_{r}}}$

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(4)

The velocity of light in vacuum is given by

$c = \frac{1}{\sqrt{μ_{0} ε_{0}}}$ ...(i)

For any medium, velocity is

$v = \frac{1}{\sqrt{μ_{0} μ_{r} ε_{0} ε_{r}}} = \frac{1}{\sqrt{μ_{0} ε_{0}} \sqrt{μ_{r} ε_{r}}}$

Using equation (i),

$v = \frac{c}{\sqrt{μ_{r} ε_{r}}}$

Q 6 :
For a plane electromagnetic wave propagating in $x$ -direction, which one of the following combinations gives the correct possible directions for electric field $(E)$ and magnetic field $(B)$ respectively? [2021]

$- \hat{j} + \hat{k}, - \hat{j} + \hat{k}$
$\hat{j} + \hat{k}, \hat{j} + \hat{k}$
$- \hat{j} + \hat{k}, - \hat{j} - \hat{k}$
$\hat{j} + \hat{k}, - \hat{j} - \hat{k}$

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(3)

As $\vec{E}$ and $\vec{B}$ are perpendicular to each other, their dot product must be zero.

$\vec{E} \cdot \vec{B} = 0$

Also, the wave is propagating along x-axis i.e. cross product of $\vec{E} \times \vec{B}$ is along $\hat{i} .$

Out of given options, only $(- \hat{j} + \hat{k}),$ $(- \hat{j} - \hat{k})$ follow the above conditions.

Q 7 :
Light with an average flux of 20 $W / {cm}^{2}$ falls on a non-reflecting surface at normal incidence having surface area 20 ${cm}^{2}$ . The energy received by the surface during time span of 1 minute is [2020]

$10 \times 10^{3} J$
$12 \times 10^{3} J$
$24 \times 10^{3} J$
$48 \times 10^{3} J$

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(3)

Energy received in 1 minute = Intensity $\times$ Area $\times$ Time

$E = (20 {W/cm}^{2}) \times (20 {cm}^{2}) \times (1 \times 60 s) = 24 \times 10^{3} J$

Q 8 :
The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is (c = speed of electromagnetic waves) [2020]

c : 1
1 : 1
1 : c
1 : $c^{2}$

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(2)

Energy of electromagnetic wave is equally distributed in the form of electric and magnetic field energy, so ratio $\frac{U_{E}}{U_{B}} = \frac{1}{1} .$

Q 9 :
For a transparent medium relative permeability and permittivity, $μ_{r}$ and $ε_{r}$ are 1.0 and 1.44 respectively. The velocity of light in this medium would be [2019]

$2.5 \times 10^{8}$ m/s
$3 \times 10^{8}$ m/s
$2.08 \times 10^{8}$ m/s
$4.32 \times 10^{8}$ m/s

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(1)

Given: relative permittivity, $ε_{r} = 1.44$ and relative permeability, $μ_{r} = 1$

Now, as we know that, $ε_{r} = \frac{ε}{ε_{0}} \Rightarrow ε = ε_{r} ε_{0}$

and $μ_{r} = \frac{μ}{μ_{0}} \Rightarrow μ = μ_{r} μ_{0}$

where, $ε$ and $μ$ are the permittivity and permeability of the medium.

$∴$ Velocity of light in the medium will be

$v = \frac{1}{\sqrt{μ ε}} = \frac{1}{\sqrt{μ_{r} μ_{0} ε_{r} ε_{0}}} = \frac{c}{\sqrt{μ_{r} ε_{r}}} = \frac{3 \times 10^{8}}{\sqrt{1 \times 1.44}}$

$= 2.5 \times 10^{8} m/s$

Q 10 :
An em wave is propagating in a medium with a velocity $\vec{v} = v \hat{i}$ . The instantaneous oscillating electric field of this em wave is along $+ y$ axis. Then the direction of oscillating magnetic field of the em wave will be along [2018]

$- z$ direction
$+ z$ direction
$- y$ direction
$- x$ direction

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(2)

Velocity of em wave in a medium is given by $\vec{v} = \vec{E} \times \vec{B}$

$∴$ $v \hat{i} = (E \hat{j}) \times (\vec{B}) [∵ \vec{E} = E \hat{j} (Given)]$

As $\hat{i} = \hat{j} \times \hat{k}, so \vec{B} = B \hat{k}$

Direction of oscillating magnetic field of the em wave will be along $+ z$ direction.

Topic Question Set

Q 1 :
The electric field in a plane electromagnetic wave is given by $E_{z} = 60 \cos (5 x + 1.5 \times 10^{9} t) V/m .$

Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field) [2025]

Q 3 :
The property which is not of an electromagnetic wave travelling in free space is that [2024]

Q 5 :
When light propagates through a material medium of relative permittivity $ε_{r}$ and relative permeability $μ_{r}$ , the velocity of light, $v$ is given by (c - velocity of light in vacuum) [2022]

Q 6 :
For a plane electromagnetic wave propagating in $x$ -direction, which one of the following combinations gives the correct possible directions for electric field $(E)$ and magnetic field $(B)$ respectively? [2021]

Q 7 :
Light with an average flux of 20 $W / {cm}^{2}$ falls on a non-reflecting surface at normal incidence having surface area 20 ${cm}^{2}$ . The energy received by the surface during time span of 1 minute is [2020]

Q 8 :
The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is (c = speed of electromagnetic waves) [2020]

Q 9 :
For a transparent medium relative permeability and permittivity, $μ_{r}$ and $ε_{r}$ are 1.0 and 1.44 respectively. The velocity of light in this medium would be [2019]

Q 10 :
An em wave is propagating in a medium with a velocity $\vec{v} = v \hat{i}$ . The instantaneous oscillating electric field of this em wave is along $+ y$ axis. Then the direction of oscillating magnetic field of the em wave will be along [2018]

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Topic Question Set

Q 1 : The electric field in a plane electromagnetic wave is given by Ez=60cos(5x+1.5×109t) V/m. Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field) [2025]

Q 2 : If the ratio of relative permeability and relative permittivity of a uniform medium is 1 : 4. The ratio of the magnitudes of electric field intensity (E) to the magnetic field intensity (H) of an EM wave propagating in that medium is (Given that μ0ε0=120π) [2024]

Q 3 : The property which is not of an electromagnetic wave travelling in free space is that [2024]

Q 4 : In a plane electromagnetic wave travelling in free space, the electric field component oscillates sinusoidally at a frequency of 2.0×1010 Hz and amplitude 48 Vm-1. Then the amplitude of oscillating magnetic field is (Speed of light in free space = 3×108 ms-1) [2023]

Q 5 : When light propagates through a material medium of relative permittivity εr and relative permeability μr, the velocity of light, v is given by (c - velocity of light in vacuum) [2022]

Q 6 : For a plane electromagnetic wave propagating in x-direction, which one of the following combinations gives the correct possible directions for electric field (E) and magnetic field (B) respectively? [2021]

Q 7 : Light with an average flux of 20 W/cm2 falls on a non-reflecting surface at normal incidence having surface area 20 cm2. The energy received by the surface during time span of 1 minute is [2020]

Q 8 : The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is (c = speed of electromagnetic waves) [2020]

Q 9 : For a transparent medium relative permeability and permittivity, μr and εr are 1.0 and 1.44 respectively. The velocity of light in this medium would be [2019]

Q 10 : An em wave is propagating in a medium with a velocity v→=vi^. The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along [2018]

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Q 1 :
The electric field in a plane electromagnetic wave is given by $E_{z} = 60 \cos (5 x + 1.5 \times 10^{9} t) V/m .$

Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field) [2025]

Q 3 :
The property which is not of an electromagnetic wave travelling in free space is that [2024]

Q 5 :
When light propagates through a material medium of relative permittivity $ε_{r}$ and relative permeability $μ_{r}$ , the velocity of light, $v$ is given by (c - velocity of light in vacuum) [2022]

Q 6 :
For a plane electromagnetic wave propagating in $x$ -direction, which one of the following combinations gives the correct possible directions for electric field $(E)$ and magnetic field $(B)$ respectively? [2021]

Q 7 :
Light with an average flux of 20 $W / {cm}^{2}$ falls on a non-reflecting surface at normal incidence having surface area 20 ${cm}^{2}$ . The energy received by the surface during time span of 1 minute is [2020]

Q 8 :
The ratio of contributions made by the electric field and magnetic field components to the intensity of an electromagnetic wave is (c = speed of electromagnetic waves) [2020]

Q 9 :
For a transparent medium relative permeability and permittivity, $μ_{r}$ and $ε_{r}$ are 1.0 and 1.44 respectively. The velocity of light in this medium would be [2019]

Q 10 :
An em wave is propagating in a medium with a velocity $\vec{v} = v \hat{i}$ . The instantaneous oscillating electric field of this em wave is along $+ y$ axis. Then the direction of oscillating magnetic field of the em wave will be along [2018]