Question

Is it always necessary to use red light to get photoelectric emission?

Hint:

Check the metal’s work function; use \( \nu>\frac{\phi}{h} \) to ensure photoelectric emission.

Answer 1

Photoelectric emission occurs when the frequency of incident light exceeds the threshold frequency \( \nu_0 \) of the metal, where \( h\nu \geq \phi \) (\( \phi \) is the work function). Red light has the lowest frequency in the visible spectrum (\( \approx 4 \times 10^{14} \, \text{Hz} \)). If the metal’s threshold frequency is higher than that of red light, emission will not occur. Higher frequency light (e.g., blue, violet, or ultraviolet) is often required.
Answer: No, red light is not always necessary; light with frequency above the metal’s threshold frequency is needed.