Question

A cesium photocell, with a steady potential difference of 60 V across, is illuminated by a bright point source of light 50 cm away. When the same light is placed 1 m away, the photoelectrons emitted from the cell-

• A. Are one quarter as numerous
• B. Are half as numerous
• C. Each carry one quarter of their previous momentum
• D. Each carry one quarter of their previous energy

Answer 1

Answer: (A)

Are one quarter as numerous

Answer 2

d₁ = 50 cm

d₂ = 1m = 100 cm

d₂ = 2d₁ $\left( \mathrm { I } \propto \frac { 1 } { \mathrm {~d} ^ { 2 } } \right)$

I₂ = I₁/4

$\mathrm { n } _ { \mathrm { Ph } _ { 2 } }$ = $\frac { \mathrm { n } _ { \mathrm { Ph } _ { 1 } } } { 4 }$

$\mathrm { n } _ { \mathrm { e } _ { 2 } }$ = $\frac { \mathrm { n } _ { \mathrm { e } _ { 1 } } } { 4 }$