Wave Equation of EM Waves

Q.

A laser beam can be focussed on an area equal to the square of its wavelength. A He-Ne laser radiates energy at the rate of 1mW and its wavelength is 632.8 nm. The intensity of focussed beam will be

1. $1.5\times {10}^{13}W/m^2$

2. $2.5\times {10}^{9}W/m^2$

3. $3.5\times {10}^{17}W/m^2$

4. None of these

Q. The 21 cm radio wave emitted by hydrogen in interstellar space is due to the interaction called the hyperfine interaction is atomic hydrogen. The energy of the emitted wave is nearly

1. ${10}^{-17}$ Joule
2. 1 Joule
3. $7\times {10}^{-8}$ Joule
4. ${10}^{-24}$ Joule

Q. Which of the following represents an infrared wavelength

1. ${10}^{-4}$
2. ${10}^{-5}$
3. ${10}^{-6}$
4. ${10}^{-7}$

Q. Television signals broadcast from the moon can be received on the earth while the TV broadcast from Delhi cannot be received at places about 100 km distant from Delhi. This is because

1. There is no atmosphere around the moon
2. Of strong gravity effect on TV signals
3. TV signals travel straight and cannot follow the curvature of the earth
4. There is atmosphere around the earth

Q.

In an electromagnetic wave, the amplitude of electric field is 1 V/m. the frequency of wave is $5\times {10}^{14}$Hz. The wave is propagating along z-axis. The average energy density of electric field, in $Joule{m}^3$, will be

1. $1.1\times {10}^{-11}$

2. $2.2\times {10}^{-12}$

3. $3.3\times {10}^{-13}$

4. $4.4\times {10}^{-14}$

Q. In SI unit, the electric field of an E.M wave in free space is described by $E_y=400\sin \left[\pi \right({10}^{6}x-2ft\left)\right]$. Here, $f$ is the frequency.

1. Wave length of light is 2000 nm.
2. Frequency is $1.5\times {10}^{14}$ Hz.
3. This E.M wave is not visible for human eyes.
4. All of the above

Q.

In an electromagnetic wave, the electric and magnetising fields are 100V $m^{-1}$ and 0.265 $A{m}^{-1}$. The maximum energy flow is

1. 26.5 $W/m^2$

2. 36.5 $W/m^2$

3. 46.7 $W/m^2$

4. 765 $W/m^2$

Q. Direction of propagation of light is perpendicular to the plane containing electric and magnetic field.

1. False
2. True

Q.

Radiations of intensity $0.5W/m^2$ are striking a metal plate. The pressure on the plate is

1. $0.166\times {10}^{-8}N/m^2$

2. $0.332\times {10}^{-8}N/m^2$

3. $0.111\times {10}^{-8}N/m^2$

4. $0.083\times {10}^{-8}N/m^2$

Q.

A radio receiver antenna that is 2 m long is oriented along the direction of the electromagnetic wave and receives a signal of intensity $5\times {10}^{-16}W/m^2$. The maximum instantaneous potential difference across the two ends of the antenna is

1. 1.23 mV

2. 1.23 mV

3. 1.23 V

4. 12.3 mV

Q.

A plane electromagnetic wave of wave intensity 6 $W/m^2$strikes a small mirror area 40 $c{m}^2$, held perpendicular to the approaching wave. The momentum transferred by the wave to the mirror each second will be

1. $6.4\times {10}^{-7}kg-m/s^2$

2. $4.8\times {10}^{-8}kg-m/s^2$

3. $3.2\times {10}^{-9}kg-m/s^2$

4. $1.6\times {10}^{-10}kg-m/s^2$

Q.

TV waves have a wavelength range of 1-10 meter. Their frequency range in MHz is

1. 30-300

2. 3-30

3. 300-3000

4. 3-3000

Q.

An electromagnetic wave of v = 3MHz passes from vacuum into dielectric medium with $ϵ=4.0{ϵ}_0.$ Then:

1. wavelength is doubled and frequency becomes half

2. wavelength is doubled and frequency same.

3. wavelength and frequency both remain unchanged

4. wavelength is halved but frequency remains same.

Q. If a source is transmitting electromagnetic wave of frequency $8.2\times {10}^6$ Hz, then wavelength of the electromagnetic waves transmitted from the source will be

1. 36.6 m
2. 40.5 m
3. 42.3 m
4. 50.9 m

Q.

The intensity of gamma radiation from a given source is I. On passing through 36 mm of lead, it is reduced to $\frac{I}{8}$. The thickness of lead which will reduce the intensity to $\frac{l}{2}$ will be

1. 18 mm

2. 12 mm

3. 6 mm

4. 9 mm

Q.

In an electromagnetic wave, the amplitude of electric field is 1 V/m. the frequency of wave is $5\times {10}^{14}$Hz. The wave is propagating along z-axis. The average energy density of electric field, in $Joule{m}^3$, will be

1. $1.1\times {10}^{-11}$

2. $2.2\times {10}^{-12}$

3. $3.3\times {10}^{-13}$

4. $4.4\times {10}^{-14}$

Q. If a source is transmitting electromagnetic wave of frequency $8.2\times {10}^6$ Hz, then wavelength of the electromagnetic waves transmitted from the source will be

1. 36.6 m
2. 40.5 m
3. 42.3 m
4. 50.9 m

Q.

A plane electromagnetic wave of wave intensity 6 $W/m^2$strikes a small mirror area 40 $c{m}^2$, held perpendicular to the approaching wave. The momentum transferred by the wave to the mirror each second will be

1. $6.4\times {10}^{-7}kg-m/s^2$

2. $4.8\times {10}^{-8}kg-m/s^2$

3. $3.2\times {10}^{-9}kg-m/s^2$

4. $1.6\times {10}^{-10}kg-m/s^2$

Q.

A radio receiver antenna that is 2 m long is oriented along the direction of the electromagnetic wave and receives a signal of intensity $5\times {10}^{-16}W/m^2$. The maximum instantaneous potential difference across the two ends of the antenna is

1. 1.23 mV

2. 1.23 mV

3. 1.23 V

4. 12.3 mV