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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

`36 xx 10^(-5) "kg m/s"`

B

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

C

`108 xx 10^(4) "kg m/s"`

D

`1.08 xx 10^(7) "kg m/s"`

Text Solution

Verified by Experts

The correct Answer is:
B
For complete absorption, `p = (U)/(c)`
where U = Energy carried by light `= IAt`
`:. p = (IA t)/(c)`
Here, `I = 20 W//cm^(2), A = 30 cm^(2), t = 30 min = 1800 s`
So, `p = (20 xx 30 xx 1800)/(3 xx 10^(8)) = 36 xx 10^(-4) kg m s^(-1)`
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