A plate of mass `10 gm` is in equillibrium in air due to the force exterted by light beam on plate. Calculate powder of beam. Assume plates is perfectly absorbing.

Explanation

Since plate is in air, so gravitational force will act on this
`F_("gravitaional")=mg` (dowmward)
`=10xx10^(-3)xx 10`
`10^(-1)N`
for the equilibrium force exterted by light beam should be equal to `F_("gravitational")`
`F_("Photon")=F_("gravitaional")`
Let power of light beam be `P`
`:. F_("photon")=(P)/(c )`
`:. (P)/(c )=10^(-1) P=3.0xx10^(8)xx10^(-1)`
`P=3xx10^(7)W`