In a photoelectric effect experiment, the graph of stopping potential V versus reciprocal of wavelength obtained is shown in the figure. As the intensity of incident radiation is increased :

Solution

Physics sir · 4 steps

Write the equation of this line first: neither its slope nor its intercept contains intensity.

1. Einstein's equation. The fastest electron is stopped when eV = hc/λ - φ, where φ is the work function of the metal. Divide by e to get V as a function of 1/λ.

   V = hc/e(1/λ) - φ/e

2. Read the graph. This is a straight line with slope tan θ = hc/e, a combination of constants. It cuts the 1/λ axis at 1/λ₀ = φ/hc, which depends only on the metal.
3. Role of intensity. Higher intensity means more photons per second, so more electrons come out and the photocurrent rises. Each photon still carries the same energy hc/λ, so the maximum kinetic energy, and with it V, stays the same.
4. So. The slope and the intercept are both unchanged, so the graph does not change. The answer is (b).

The idea to keep. Stopping potential depends only on the frequency of the light and the metal's work function. Intensity changes the photocurrent, never the stopping potential.

Answer from the NTA final answer key. Solution by PrepWiser.