Find the average force (in `muN`) exerted on a `20 cm^2` non reflecting surface by the normal incidence of light whose energy flux is `18 W·cm^(-2)` which enacts for a duration of 30 min:

Answer

`01.20 `

Explanation

Total energy falling on surface,
`U= 18 xx 20 xx 30 xx 60J `
Momentum transported by wave `p = U/c`
`therefore` Average force exerted, `F = p/t = U/(ct)`
`= (18 xx 20 xx 30 xx 60)/(3 xx 10^8 xx 30 xx 60)`
`= 1.2 xx 10^(-6) N`
`= 1.2 mu N`