# Intensity in Photon Model

## Trending Questions

**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

**Q.**Monochromatic light of frequency of 6×1014 Hz is produced by a laser. Power emitted is 2×10−3W. Approximately how many photons per second are emitted by the source?

- 5×1013
- 5×1014
- 5×1015
- 5×1016

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

- 3.33×10−8N
- 6.67×10−8N
- 2×10−8N
- 5×10−8N

**Q.**

A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 12m away, the number of electrons emitted by photo cathode would

Decrease by a factor of 2

Increase by a factor of 2

Decrease by a factor of 4

Increase by a factor of 4

**Q.**The minimum intensity of light to be detected by human eye is 10−10W/m2. The number of photons of wavelength 5.6×10−7m entering the eye, with pupil area 10−6m2, per second for vision will be nearly

- 100
- 200
- 300
- 400

**Q.**

There are n1 photons of frequency γ1 in a beam of light. In an equally energetic beam, there are n2 photons of frequency γ2 . Then the correct relation is

n1n2=1

n1n2=γ1γ2

n1n2=γ2γ1

n1n2=γ21γ22.

**Q.**

What is the conclusion of the photoelectric effect?

**Q.**

A perfect reflecting mirror of mass M mounted on a spring constitudes a spring-mass system of angular frequency Ω such that 4πMΩh=1024 m−2 with h as Planck's constant. N photons of wavelength λ=8π×10−6 m strike the mirror simultaneously at normal incidence such that the mirror gets displaced by 1 μm. If the value of N is

**Q.**

A monochromatic source of light operating at 200 W emits 4×1020 photons per second. The wavelength of this light will be

**Q.**

Which photon is more energetic red or violet and why?

**Q.**As the intensity of incident light increases

Photoelectric current increases

Photoelectric current decreases

Kinetic energy of emitted photoelectrons increases

- Kinetic energy of emitted photoelectrons decreases

**Q.**When a beam of 10.6 eV photons of intensity falls on a platinum surface of area 1.0×10−4 m2 and work function 5.6 eV. If 53% of the incident photon eject photoelectrons. Total photoelectrons emitting per second is n×1011. Find n

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

- number of electrons emitted is half of the initial number
- each emitted electron carries half the initial energy
- number of electrons emitted is a quarter of the initial number
- 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 $h=6.6\xc3\u2014{10}^{-34}Js$, speed of light $c=3.0\xc3\u2014{10}^{8}m/s$]

$5\xc3\u2014{10}^{15}$

$1.5\xc3\u2014{10}^{16}$

$1\xc3\u2014{10}^{16}$

$2\xc3\u2014{10}^{16}$

**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 ?

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

**Q.**1020 photons of wavelength 660 nm are emitted per second from a lamp. What is the wattage of the lamp if Planck's constant is equal to6.6×10−34 Js?

- 30 W
- 60 W
- 100 W
- 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

Are one quarter as numerous

Are half as numerous

Each carry one quarter of their previous momentum

Each carry one quarter of their previous energy

**Q.**A laser beam λ=633 nm has a power of 3 mW. What will be the pressure exerted on a surface by this beam if the cross-section area is 3 mm2? (Assume perfect reflection and normal incidence).

- 6.6×10−3Nm2
- 6.6×10−6Nm2
- 6.6×10−9Nm2
- 6.6Nm2

**Q.**

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

1020

1030

1040

1010

**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

- 3×1016s−1

- 9×1016s−1

- 3×1019s−1

- 9×1017s−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

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

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

Will be half in number

- Will be one-fourth in number

**Q.**

If the wavelength of light is 4000 ∘A, then the number of waves in 1 mm length will be

0.25

25

0.25×104

25×104

**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=6×10−34J−sec )

100

1000

3×1020

3×1018

**Q.**When monochromatic light falls on a photosensitive material, the number of photoelectrons emitted per second is n and their maximum kinetic energy is Kmax. If the intensity of the incident light is doubled, then

- Both n and Kmax are doubled.

- Both n and Kmax are halved.

- n is doubled but Kmax remains the same.

- Kmax 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

Greater with visible light

Infinite in both cases

Greater with ultraviolet light

Equal in both cases