A beam of white light is incident normally on a plane surface absorbing `(70%)` of the light and reflecting the rest. If the incident beam carries 10 W of power , find the force exerted by it on the surface .

Explanation

` Power = 10W [ p Momentum] `
` lambda = h / p or P = h / lambda`
or , p/ t = h / lambda t `
` E = hc / lambda `
or, `E / t = hc / lambda t Power (W)`
` W = Pe / t
` or W / e = P / t (force) `
` Force = 7 / 10 (absored ) 2 + xx 3.3 / 10(reflected)`
` = 7 / 10 x x W / c + 2 xx 3 / 10 xx W / c `
` = 7 / 10 xx 10 / 3 xx 10^(8) + 2 xx 3 / 10 xx 10 / 3 xx 10^(8) `
`= 13 / 3 xx 10^(-8) = 4.33 xx 10^(-8) N`