Exams › NEET › Physics

Photoelectric work function of a metal is 1 eV. Light of wavelength λ = 3000 Å falls on it. The photoelectrons come out with velocity:

1. 10 metres/sec
2. 10² metres/sec
3. 10⁴ metres/sec
4. 10⁶ metres/sec

Correct answer: 10⁶ metres/sec

Solution

The energy of the incident photon is calculated using E = hc/λ. Substituting h = 6.63 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s, and λ = 3000 Å = 3 × 10⁻⁷ m, we find E ≈ 4.14 eV. Subtracting the work function (1 eV), the kinetic energy of the photoelectron is 3.14 eV. Using KE = 0.5mv², the velocity is approximately 10⁶ m/s.

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 →