Exams › NEET › Physics

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

Correct answer: number of electrons emitted is a quarter of the initial number

Solution

The intensity of light decreases with the square of the distance from the source (inverse square law). Since the intensity is proportional to the number of emitted electrons, doubling the distance reduces the intensity to one-fourth, and thus the number of emitted electrons also becomes one-fourth.

Related NEET Physics questions

• An α-particle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m². The wavelength associated with the particle will be:
• For photoelectric emission from certain metal the cut-off frequency is ν. If radiation of frequency 2ν impinges on the metal plate, the maximum possible velocity of the emitted electron will be (m is the electron mass)
• Light of wavelength 500 nm is incident on a metal with work function 2.28 eV. The wavelength of the emitted electron is
• A source of light is placed at a distance of 50 cm from a photocell and the stopping potential is found to be V₀. If the distance between the light source and photocell is made 25 cm, the new stopping potential will be
• A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is (h = Planck's constant, c = speed of light)
• A certain metallic surface is illuminated with monochromatic light of wavelength λ. The stopping potential for photoelectric current for this light is 3V₀. If the same surface is illuminated with light of wavelength 2λ, the stopping potential is V₀. The threshold wavelength for this surface for photo-electric effect is

⚔️ Practice NEET Physics free + battle 1v1 →