Intensity in Photon Model

Q. the energy in eV possessed by a neon atom at 27^o isa)1.72 \ast×10^{-3 }b)3.88 ×10^{-4}

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. A photoelectric cell is illuminated by a point source of light 1m away. When the source is shifted to 2m then

1. each emitted electron carries half the initial energy
2. number of electrons emitted is a quarter of the initial number
3. each emitted electron carries one quarter of the initial energy
4. number of electrons emitted is half of the initial number

Q.

How is transmitting intensity calculated?

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. Monochromatic light of wavelength $3000\stackrel{\circ }{A}$ is incident on a surface area of $4c{m}^2$. If intensity of light is $150mW{m}^{-2}$, then the rate at which photons strike the target is

1. $3\times {10}^{10}{s}^{-1}$
2. $9\times {10}^{13}{s}^{-1}$
3. $7\times {10}^{20}{s}^{-1}$
4. $6\times {10}^{19}{s}^{-1}$

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

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

3. $13.27\times {10}^{34}$

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

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.

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. ${10}^{20}$ 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. 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. 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 photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m then

1. Number of electrons emitted is half the initial number

2. Each emitted electron carries half the initial energy

3. Number of electrons emitted is a quarter of the initial number

4. Each emitted electron carries one quarter of the initial energy

Q.

The threshold wavelength for photoelectric emission from a material is $5200\stackrel{\circ }{A}$. Photo-electrons will be emitted when this material is illuminated with monochromatic radiation from a

1. 50 watt infrared lamp

2. 1 watt infrared lamp

3. 50 watt ultraviolet lamp

4. 1 watt ultraviolet lamp

5. Both (c) and (d)

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.

If the wavelength of light is $4000\stackrel{\circ }{A}$, then the number of waves in 1 mm length will be

1. $25$

2. $0.25$

3. $0.25\times {10}^4$

4. $25\times {10}^4$

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. UV light of wavelength 300 nm and intensity 1 $W{m}^{-2}$ falls on the surface of photo electric metal. If one percent of incident photons, produce photo electrons, then the number of photo electrons emitted from an area of 1.0 $c{m}^2$ of the surface is nearly

1. $2.13\times {10}^{11}{s}^{-1}$
2. $1.5\times {10}^{12}{s}^{-1}$
3. $3.02\times {10}^{12}{s}^{-1}$
4. $3\times {10}^{12}{s}^{-1}$

Q.

A point source causes photoelectric effect from a small metal plate. Which of the following curves may represent the saturation photocurrent as a function of the distance between the source and the metal?

__

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.

The number of photons emitted by a 5mW laser source operating at 632.8 nm is __$\times {10}^{16}$

Q. Consider a sphere of radius $R$ exposed to radiation of intensity $I$ as shown in figure. If surface of sphere is partially reflecting with reflection coefficient is $0.3$, then radiation force experienced is

1. $\frac{0.3\pi R^{2}I}{c}$
2. $\frac{1.3\pi R^{2}I}{c}$
3. $\frac{1.7\pi R^{2}I}{c}$
4. $\frac{\pi R^{2}I}{c}$

Q. A battery-operated torch is adjusted to send an almost parallel beam of light. It produces an illuminancle of 40 lux when the light falls on a wall 2 m away. The illuminance produced when it falls on a wall 4 m away is close to
(a) 40 lux
(b) 20 lux
(c) 10 lux
(d) 5 lux