A 5 W monochromatic light source of wavelength 5000 Å liberates electrons from a surface at 0.5 m distance. If moved to 1.0 m, emission count is reduced by a factor of:
Options

Question

A 5 W monochromatic light source of wavelength 5000 Å liberates electrons from a surface at 0.5 m distance. If moved to 1.0 m, emission count is reduced by a factor of:

G1 Physics · Accepted Answer

For a point source intensity I ∝ 1/r². Increasing distance from 0.5 m to 1.0 m doubles r, reducing intensity and electron emission rate by (0.5/1)² = 1/4. Hence reduced by factor 4. Answer: D.