Question

A photo cell is receiving light from a source placed at a distance of 1 m. If the same source is to be placed at a distance of 2 m, then the ejected electron

• A. Moves with one-fourth energy as that of the initial energy
• B. Moves with one fourth of momentum as that of the initial momentum
• C. Will be half in number
• D. Will be one-fourth in number

Answer 1

Answer: (D)

Will be one-fourth in number

Answer 2

Number of photons ∝ Intensity ∝ $\frac { 1 } { ( \text { distance } ) ^ { 2 } }$

⇒ $\frac { N _ { 1 } } { N _ { 2 } } = \left( \frac { d _ { 2 } } { d _ { 1 } } \right) ^ { 2 }$ ⇒ $N _ { 2 } = \frac { N _ { 1 } } { 4 }$.