Intensity in Photon Model

Q. Q.26 The de broglie wavelength of an electron moving with kinetic energy of 144 ev is nearly

Q.

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

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. A parallel beam of monochromatic light of wavelength $500nm$ is incident normally on a perfectly absorbing surface. The power through any cross-section of the beam is $10W$. What is the force exerted by it?

1. $3.33\times {10}^{-8}N$
2. $6.67\times {10}^{-8}N$
3. $2\times {10}^{-8}N$
4. $5\times {10}^{-8}N$

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 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.

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.

What is the conclusion of the photoelectric effect?

Q.

A monochromatic source of light operating at 200 W emits $4\times {10}^{20}$ photons per second. The wavelength of this light will be __ nm.

Q.

A perfect reflecting mirror of mass $M$ mounted on a spring constitudes a spring-mass system of angular frequency $\Omega$ such that $\frac{4\pi M\Omega }{h}={10}^{24}{m}^{-2}$ with $h$ as Planck's constant. $N$ photons of wavelength $\lambda =8\pi \times {10}^{-6}$ m strike the mirror simultaneously at normal incidence such that the mirror gets displaced by $1\mu m$. If the value of $N$ is $X\times {10}^{12}$, then the value of $X$ is [Consider the spring as massless]

Q.

Which photon is more energetic red or violet and why?

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. When a beam of $10.6\text{eV}$ photons of intensity falls on a platinum surface of area $1.0\times {10}^{-4}{\text{m}}^2$ and work function $5.6\text{eV}.$ If $53\%$ of the incident photon eject photoelectrons. Total photoelectrons emitting per second is $n\times {10}^{11}$. Find $n$(integer only)

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.

A $2mW$ laser operates at a wavelength of $500nm$. The number of photons that will be emitted per second is :[Given Plancks constant $h=6.6\times {10}^{-34}Js$, speed of light $c=3.0\times {10}^{8}m/s$]

1. $5\times {10}^{15}$

2. $1.5\times {10}^{16}$

3. $1\times {10}^{16}$

4. $2\times {10}^{16}$

Q.

The wavelength of light for the least energetic photon emitted in the Lyman series of the hydrogen atom spectrum is __________ nm

___

Q. A point source of light is used in an experiment of photoelectric effects. If the distance between the source and the photo-electric surface is doubled, which of the following may result ?

1. Photoelectric current will decrease.
2. Stopping potential will be halved
3. Maximum kinetic energy of photo-electrons will decrease.
4. Stopping potential will increase slightly.

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. 4. If the mass of neutron is 1.7into 10 to the power _27kg then the de broglie wavelength of neutron of energy 3 ev is

Q.

A caesium photocell, with a steady potential difference of 60V across, is illuminated by a bright point source of light 50 cm away. When the same light is placed 1m away the photoelectrons emitted from the cell

1. Are one quarter as numerous

2. Are half as numerous

3. Each carry one quarter of their previous momentum

4. Each carry one quarter of their previous energy

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

1. ${10}^{20}$

2. ${10}^{30}$

3. ${10}^{40}$

4. ${10}^{10}$

Q. Monochromatic light of wavelength 667 nm is produced by a laser lamp. The power emitted is 9 mW. The number of photons arriving per second on the average at a target irradiated by this beam is

1. $3\times {10}^{16}{s}^{-1}$
   
2. $9\times {10}^{16}{s}^{-1}$
   
3. $3\times {10}^{19}{s}^{-1}$
   
4. $9\times {10}^{17}{s}^{-1}$
   

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. 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.

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

1. $0.25$

2. $25$

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

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

Q.

Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW.

(a) Find the energy and momentum of each photon in the light beam,

(b) How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area), and

(c) How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?

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. When monochromatic light falls on a photosensitive material, the number of photoelectrons emitted per second is $n$ and their maximum kinetic energy is $K_{max}$. If the intensity of the incident light is doubled, then

1. Both $n$ and $K_{max}$ are doubled.
   
2. Both $n$ and $K_{max}$ are halved.
   
3. $n$ is doubled but $K_{max}$ remains the same.
   
4. $K_{max}$ is doubled but $n$ remains the same.
   

Q.

Sodium surface is illuminated by ultraviolet and visible radiation successively and the stopping potential determined. The stopping potential is

1. Greater with visible light

2. Infinite in both cases

3. Greater with ultraviolet light

4. Equal in both cases