Intensity in Photon Model

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. Will be half in number
3. Moves with one fourth of momentum as that of the initial momentum
4. Will be one-fourth in number

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 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.

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

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_b.

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

1. number of electrons emitted is half of 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. 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.

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