Intensity in Photon Model

Q.

A radio transmitter operates at a frequency of 880 kHz and a power of 10 kW. The number of photons emitted per second are

1. $13.27\times {10}^{34}$

2. $1327\times {10}^{34}$

3. $1.72\times {10}^{31}$

4. $0.075\times {10}^{-34}$

Q.

An AIR station is broadcasting the waves of wavelength 300 metres. If the radiating power of the transmitter is 10 kW, then the number of photons radiated per second is

1. $1.5\times {10}^{35}$

2. $1.5\times {10}^{29}$

3. $1.5\times {10}^{31}$

4. $1.5\times {10}^{33}$

Q.

The work function of aluminium is 4.2 eV.If two photons, each of energy 3.5 eVstrike an electron of aluminium, then emission of electrons will be

1. Possible

2. Not possible

3. Data is incomplete

4. Depend upon the density of the surface

Q. A laser beam $\lambda =633nm$ has a power of $3mW$. What will be the pressure exerted on a surface by this beam if the cross-section area is $3m{m}^2$? (Assume perfect reflection and normal incidence).

1. $6.6\times {10}^{-3}\frac{N}{m^2}$
2. $6.6\times {10}^{-6}\frac{N}{m^2}$
3. $6.6\times {10}^{-9}\frac{N}{m^2}$
4. $6.6\frac{N}{m^2}$

Q.

A beam of light of wavelength $\lambda$ and with illumination L falls on a clean surface of sodium. If N photoelectrons are emitted each with kinetic energy E, then

1. $N\propto LandE\propto L$

2. $N\propto LandE\propto \frac{1}{\lambda }$

3. $N\propto \lambda andE\propto L$

4. $N\propto \frac{1}{\lambda }andE\propto \frac{1}{L}$

Q.

In photoelectric effect if the intensity of light is doubled then maximum kinetic energy of photoelectrons will become

1. Double

2. Half

3. Four time

4. No change

Q. Monochromatic light of frequency of $6\times {10}^{14}Hz$ is produced by a laser. Power emitted is $2\times {10}^{-3}W.$ Approximately how many photons per second are emitted by the source?

1. $5\times {10}^{13}$
2. $5\times {10}^{14}$
3. $5\times {10}^{15}$
4. $5\times {10}^{16}$

Q. Perfectly reflecting mirror of mass $M$ mounted on a spring constitutes a spring mass system of angular frequency $\Omega ,$ such that $\frac{4\pi M\Omega }{h}={10}^{34}{m}^{-3},$ where $h$ is planck constant, $N$ photons of wavelength $\lambda =8\pi \times {10}^{-6}\text{m}$ strikes the mirror simultaneously at normal incidence such that the mirror gets displaced by $1\mu m.$ If the value of $N$ is $x\times {10}^{-2},$ then the value of $x$ is

Q.

A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed $\frac{1}{2}m$ away, the number of electrons emitted by photo cathode would

1. Decrease by a factor of 2

2. Increase by a factor of 2

3. Decrease by a factor of 4

4. Increase by a factor of 4

Q.

The number of photo-electrons emitted per second from a metal surface increases when

1. The energy of incident photons increases

2. The frequency of incident light increases

3. The wavelength of the incident light increases

4. The intensity of the incident light increases

Q.

A radio transmitter radiates 1 kW power at a wavelength 198.6 metres. How many photons does it emit per second

1. ${10}^{10}$

2. ${10}^{20}$

3. ${10}^{30}$

4. ${10}^{40}$

Q. The minimum intensity of light to be detected by human eye is ${10}^{-10}W/m^2$. The number of photons of wavelength $5.6\times {10}^{-7}m$ entering the eye, with pupil area ${10}^{-6}{m}^2$, per second for vision will be nearly

1. 100
2. 200
3. 300
4. 400

Q.

A beam of light of wavelength $\lambda$ and with illumination L falls on a clean surface of sodium. If N photoelectrons are emitted each with kinetic energy E, then

1. $N\propto LandE\propto L$

2. $N\propto LandE\propto \frac{1}{\lambda }$

3. $N\propto \lambda andE\propto L$

4. $N\propto \frac{1}{\lambda }andE\propto \frac{1}{L}$

Q.

A photo cell is receiving light from a source placed at a distance of 1 m. If the same source is to be placed at a distance of 2 m, then the ejected electron

1. Moves with one-fourth energy as that of the initial energy

2. Moves with one-fourth of momentum as that of the initial momentum

3. Will be half in number

4. Will be one-fourth in number

Q.

The number of photons of wavelength 540 nm emitted per second by an electric bulb of power 100W is (taking h = $h=6\times {10}^{-34}J-sec$ )

1. $100$

2. $1000$

3. $3\times {10}^{20}$

4. $3\times {10}^{18}$

Q.

An AIR station is broadcasting the waves of wavelength 300 metres. If the radiating power of the transmitter is 10 kW, then the number of photons radiated per second is

1. $1.5\times {10}^{29}$

2. $1.5\times {10}^{31}$

3. $1.5\times {10}^{33}$

4. $1.5\times {10}^{35}$

Q.

There are $n_1$ photons of frequency ${\gamma }_1$ in a beam of light. In an equally energetic beam, there are $n_2$ photons of frequency ${\gamma }_2$ . Then the correct relation is

1. $\frac{n_1}{n_2}=1$

2. $\frac{n_1}{n_2}=\frac{{\gamma }_1}{{\gamma }_2}$

3. $\frac{n_1}{n_2}=\frac{{\gamma }_2}{{\gamma }_1}$

4. $\frac{n_1}{n_2}=\frac{{\gamma }_1^2}{{\gamma }_2^2}$.

Q.

As the intensity of incident light increases

1. Photoelectric current increases

2. Photoelectric current decreases

3. Kinetic energy of emitted photoelectrons increases

4. Kinetic energy of emitted photoelectrons decreases

Q. ${10}^{20}$ photons of wavelength $660nm$ are emitted per second from a lamp. What is the wattage of the lamp if Planck's constant is equal to$6.6\times {10}^{-34}$ Js?

1. 30 W
2. 60 W
3. 100 W
4. 500 W

Q. A sodium lamp emits $3.14\times {10}^{20}$ photons per second. Calculate the distance from the sodium lamp where flux of photon is one photon per second per $c{m}^2$

1. $5cm$
2. $5\times {10}^{9}cm$
3. $10cm$
4. ${10}^{7}cm$

Q.

Let $n_r$ and $n_b$ be respectively the number of photons emitted by a red bulb and a blue bulb of equal power in one second.

1. $n_r=n_b$

2. $n_r<n_b$

3. $n_r>n_b$

4. The information is insufficient to get a relation between $n_{r}and{n}_r.$

Q.

As the intensity of incident light increases

1. Photoelectric current increases

2. Photoelectric current decreases

3. Kinetic energy of emitted photoelectrons increases

4. Kinetic energy of emitted photoelectrons decreases