When monochromatic radiation of intensity I falls on a metal surface, the number of photoelectron and their maximum kinetic energy are N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively

When monochromatic radiation of intensity I falls on a metal surface, the number of photoelectron and their maximum kinetic energy are N and T respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively Correct Answer 2N and T

CONCEPT:

• Photons: Light is said to be made up of small packets known as photons. The energy of each photon is given as

E = hν 

ν is the frequency of lightwave, h is Planck's constant.

• Photoelectrons: The electrons emitted from the metal when a ray of light incident on it is known as a photoelectron. This phenomenon is known as the photoelectric effect.
• The maximum kinetic energy of electron depends upon the energy of photons falling on the metal surface.

K = hν - ϕ 

where ϕ is the minimum energy required to emit an electron out of metal.

• More Photons will make more photoelectron to eject but the energy of photoelectron will depend upon the energy of the incident photon and not on the number of photons.
• Intensity: Intensity is defined as the number of photons per unit area. It depends upon the number of photons.

I = n /A

n = number of the photon, A = Area where the photon is falling

If the area is fixed, I ∝ n

EXPLANATION:

• The number of photoelectrons depends upon the number of photons. The number of Photons is directly proportional to intensity for a given area. 
  • So, if the intensity is doubled (from I to 2I), the number of electrons will be doubled from N to 2N.
• But the energy of a single photon is independent of intensity it will not be affected and hence the energy of the photoelectron will remain the same. 
• So, the number increased to 2N and energy remains T.