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Light with an energy flux 20 W//cm^2 fal...

Light with an energy flux` 20 W//cm^2` falls on a non-reflecting surface at normal incidence. If the surface has an area of `30 cm^2`. the total momentum delivered ( for complete absorption)during 30 minutes is

A

`36xx10^(-5)kg-m//s`

B

`36xx10^(-4)kg-m//s`

C

`108xx10^(4)kg-m//s`

D

`1.08xx10^(7)kg-m//s`

Text Solution

Verified by Experts

The correct Answer is:
B
Given, energy flux `phi=20W//cm^(2)`
Area, `A=30cm^(2)`
Time, `t=30 min=30xx60s`
Now, total energy falling on the surface in time `t` is
`U=phiAt=20xx30xx(30xx60)J`
Momentum of the incident light `=(U)/(c )`
`=(20xx30xx(30xx60))/(3xx10^(8))implies =36xx10^(-4)kg-ms^(-1)`
Momentum of the reflected light `=0`
`:. ` Momentum delivered to the surface
`=36xx10^(-4)-0=36xx10^(-4)kg-ms^(-1)`
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