Question

The work function of a metal 3eV. The colour of the visible light that is required to cause emission of photo electrons is:

• A. Yellow
• B. Blue
• C. Red
• D. Green

Hint:

In the photoelectric effect, light with frequency greater than the threshold frequency causes the emission of photoelectrons.

Answer 1

The Correct Option is B

The photoelectric effect is explained by the equation: \[ E_{\text{photon}} = h \cdot f = \text{Work Function} + K_{\text{max}} \] Here, \( E_{\text{photon}} \) is the incident light's energy, \( h \) is Planck's constant, \( f \) is the light's frequency, and \( K_{\text{max}} \) is the maximum kinetic energy of emitted photoelectrons. For photoelectron emission, the incident photon energy must meet or exceed the metal's work function. The metal's work function is given as 3eV. Thus, the photon energy must be at least 3eV to cause photoelectron emission. The relationship between photon energy and frequency is: \[ E = h \cdot f \] With \( E = 3 \, \text{eV} \). For visible light, blue light corresponds to the frequency required to achieve electron emission at 3eV. Consequently, the light's color is blue.