Electromagnetic Waves

Q. For a plane electromagnetic wave propagating in $x$-direction, which one of the following combination gives the correct possible directions for electric field $\left(E\right)$ and magnetic field $\left(B\right)$ respectively?

1. $-\hat{j}+\hat{k},-\hat{j}+\hat{k}$
2. $\hat{j}+\hat{k},\hat{j}+\hat{k}$
3. $-\hat{j}+\hat{k},-\hat{j}-\hat{k}$
4. $\hat{j}+\hat{k},-\hat{j}-\hat{k}$

Q. The magnetic field of an electromagnetic wave is given by:
$\overrightarrow{B}=1.6\times {10}^{-6}\cos (2\times {10}^{7}z+6\times {10}^{15}t)(2\hat{i}+\hat{j})\frac{\text{Wb}}{{\text{m}}^2}$

The associated electric field will be:

1. $\overrightarrow{E}=4.8\times {10}^2\cos (2\times {10}^{7}z+6\times {10}^{15}t)(\hat{i}-2\hat{j})\frac{\text{V}}{\text{m}}$
2. $\overrightarrow{E}=4.8\times {10}^2\cos (2\times {10}^{7}z+6\times {10}^{15}t)(-\hat{i}+2\hat{j})\frac{\text{V}}{\text{m}}$
3. $\overrightarrow{E}=4.8\times {10}^2\cos (2\times {10}^{7}z-6\times {10}^{15}t)(2\hat{i}+\hat{j})\frac{\text{V}}{\text{m}}$
4. $\overrightarrow{E}=4.8\times {10}^2\cos (2\times {10}^{7}z-6\times {10}^{15}t)(-2\hat{j}+\hat{i})\frac{\text{V}}{\text{m}}$

Q.

Which of the following are not electromagnetic waves?

1. Cosmic rays

2. Gamma rays

3. Beta rays

4. X-rays

Q.

Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line-of-sight communication? A TV transmitting antenna is 81m tall. How much service area can it cover if the receiving antenna is at the ground level?

Q. An electromagnetic wave has an electric field given by the expression (in Cartesian co-ordinates) : $\overrightarrow{E}(x,t)=6.0\text{cos}(1.4\times {10}^{7}x-3.43\times {10}^{15}t)\hat{z}$. What is the direction of the magnetic field at time t = 0 and position x = 0 ?

1. -x
2. +x
3. +y
4. -y

Q.

A free electron is placed in the path of a plane electromagnetic wave. The electron will start moving

a)Along the electric field

b)Along the magnetic field

c) Along the propagation of the wave

d) In the plane containing magnetic field and propagation of the wave.

Q. Determine the direction of Poynting vector for an electromagnetic wave when its electric field component is oscillating in the $+y$ direction and the magnetic field component oscillates in the $-z$ direction.

1. $-\hat{i}$
2. $\hat{i}$
3. $\hat{j}$
4. $-\hat{j}$

Q. A plane electromagnetic wave propagating along $y-$direction can have the following pair of electric field $\left(\overrightarrow{E}\right)$ and magnetic field $\left(\overrightarrow{B}\right)$ components -

1. $E_x,B_z$ or $E_z,B_x$
   
2. $E_y,B_x$ or $E_x,B_y$
   
3. $E_y,B_y$ or $E_x,B_x$
   
4. $E_y,B_y$ or $E_z,B_z$
   

Q. The size of antenna should be at least .

1. $\lambda$/10
2. $\lambda$/4
3. $\lambda$/5

Q. A plane electromagnetic wave of frequency $25\text{GHz}$ is propagating in vacuum along the $z-$direction. At a particular point in space and time, the magnetic field is given by $\overrightarrow{B}=5\times {10}^{-8}\hat{j}\text{T}.$ The corresponding electric field $\overrightarrow{E}$ is $\text{(speed of light c}=3\times {10}^8{\text{ms}}^{-1})$

1. $1.66\times {10}^{-16}\hat{i}\text{V/m}$
2. $-1.66\times {10}^{-16}\hat{i}\text{V/m}$
3. $-15\hat{i}\text{V/m}$
4. $15\hat{i}\text{V/m}$

Q. For an efficient transmission of $100MHz$ frequency, the minimum required length of antenna should be _____

1. $3m$
2. $10m$
3. $\frac{3}{4}m$
4. $100m$

Q. If $\overrightarrow{E}$ and $\overrightarrow{B}$ are the electric and magnetic field vectors of electromagnetic waves then the direction of propagation of electromagnetic wave is along the direction of:

1. $\overrightarrow{B}$
2. $\overrightarrow{E}\times \overrightarrow{B}$
3. $\overrightarrow{E}$
4. None of the above

Q. The amplitudes of electric and magnetic fields related to each other are

1. $E_0=B_0$
2. $E_0=c{B}_0$
3. $E_0=\frac{B_0}{c}$
4. $E_0=\frac{c}{B_0}$

Q. The relation between electric field $E$ and magnetic field $H$ in electromagnetic wave is:

1. $E=\frac{{\mu }_0}{{\epsilon }_0}H$
2. $E=H$
3. $E=\sqrt{\frac{{\mu }_0}{{\epsilon }_0}}H$
4. $E=\sqrt{\frac{{\epsilon }_0}{{\mu }_0}}H$

Q. How are electromagnetic waves produced? What is the source of energy of these waves? Write mathematical expressions for electric and magnetic fields of an electromagnetic wave propagating along the z-axis. Write any two important properties of electromagnetic waves.

Q. An electromagnetic wave has energy in the form of

1. variable electric field
2. variable magnetic field
3. both A and B
4. none of the above

Q. What should be minimum length of antenna for efficient transmission of signals of wavelength?

1. $\frac{\lambda }{2}$
2. $\frac{\lambda }{3}$
3. $\frac{\lambda }{4}$
4. $\frac{\lambda }{5}$

Q. A transmitting antenna at the top of a tower height 32m and that of the receiving is 50m what is the max. distance b/w them for satisfactory communication in LOSmode ?

Q. Draw propagation diagram of a linearly polarised electromagnetic wave and write any two properties of electromagnetic waves.
The amplitude of the magnetic field associated with an electromagnetic wave in vacuum is $B_0=50\times {10}^{-8}$ tesla. Write the value of amplitude of the electric field in $V/m$ associated with the wave.

Q.

Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line-of-sight communication? A TV transmitting antenna is 81m tall. How much service area can it cover if the receiving antenna is at the ground level?

Q.

Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

Q. How the effective power radiated by an antenna will be changed if the wavelength of radiation is decreased?

Q. A TV transmitting antenna is 80 m tall. If the receiving antenna is on the ground the service area is :

1. 3215 sq km
2. 144sq km
3. 12 sq km
4. 32 sq km

Q. The size of antenna should be at least .

1. $\lambda$/10
2. $\lambda$/4
3. $\lambda$/5

Q. A transmitting antenna is at a height of $40m$ and the receiving antenna is at a height of $60m.$ The maximum distance between them for satisfactory communication is nearly

1. $22.5km$
2. $27.5km$
3. $50km$
4. $25km$

Q. Advantage of HF transmission is
A) that the length of antenna is small
B) that the antenna can be mounted at larger heights
C) that the power radiated is more for a given length of antenna

1. a, b & c
2. a & c
3. b & c
4. a & b

Q. Two coherent point sources S₁ and S_2, vibrating in phase, emit light of wavelength . The separation between the sources is . Consider a line passing through S₂ and perpendicular to the line S₁ S₂. What is the smallest distance from S₂ where a minimum intensity occurs?

Q.

Isit necessary for a transmitting antenna to be at the same heightas that of the receiving antenna for line-of-sight communication? ATV transmitting antenna is 81m tall. How much service area can itcover if the receiving antenna is at the ground level?

Q. The height of transmitting antenna is (320$\times$k) meter, if the TV telecast is to cover a radius of 128 Km. Find the value of K.

Q. A plane electromagnetic wave travels in free space. Then the ratio of the magnitudes of electric and magnetic fields at a point is equal to:

1. inverse of the velocity of the electromagnetic wave
2. inverse of the energy of electromagnetic wave
3. velocity of electromagnetic wave
4. energy of electromagnetic wave