If electromagnetic waves of power $600 \ W$ are incident on a non-reflecting surface,then the total force acting on the surface is

$A$ small mirror of mass $m$ is suspended by a massless thread of length $l$. Find the small angle through which the thread will be deflected when a short pulse of laser of energy $E$ falls normally on the mirror. ($c=$ speed of light in vacuum and $g=$ acceleration due to gravity)

$A$ light of intensity $12 W m^{-2}$ is incident on a black surface of area $4 cm^2$. The radiation pressure on the surface is

$A$ $1.5 \,kW$ laser beam of wavelength $6400 \,\mathring A$ is used to levitate a thin aluminium disc of the same area as the cross-section of the beam. The laser light is reflected by the aluminium disc without any absorption. The mass of the foil is close to ......... $kg$.

Light with an intensity of $18 \ W \ m^{-2}$ is incident normally on an opaque surface. If the area of the surface is $20 \ m^2$,calculate the average force exerted on the surface in $30 \ min$.

$A$ totally reflecting small plane mirror placed horizontally faces a parallel beam of light as shown in the figure. The mass of the mirror is $20 \, g$. Assume that there is no absorption in the lens and that $30 \%$ of the light emitted by the source goes through the lens. Find the power of the source needed to support the weight of the mirror in $MW$ (take $g = 10 \, m/s^2$ and $c = 3 \times 10^8 \, m/s$):-