A lamp is placed at a distance of 8 cm from a photocell and the microammeter records a current of `100 mu A`. If the lamp is kept at a distance of 4 cm from the photocell, the photoelectric current recorded by the microammeter will be

Options

A. `200 mu A`
B. `400 mu A`
C. `100 mu A`
D. `300 mu A`

Answer

B

Explanation

Photoelectric current `prop` intensity and Intensity `prop (1)/(("dist")^(2))`
`:.(I_(2))/(I_(1))=(d_(1)^(2))/(d_(2)^(2))=(8^(2))/(4^(2))=4/1`
`:.I_(2)=4I_(1)=40 muA`