$A$ point source of light is placed at the centre of curvature of a hemispherical surface. The source emits a power of $24 \, W$. The radius of curvature of the hemisphere is $10 \, cm$ and the inner surface is completely reflecting. The force on the hemisphere due to the light falling on it is $.......... \times 10^{-8} \, N$.

$A$ radiation of energy $E$ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is ($C =$ velocity of light).

An impulse laser may be treated as a source of photons that are emitted during the time interval of the pulse,which is followed by a time interval when no photons are produced. Pulses are periodically repeated. $A$ laser beam of diameter $d = 10 \, \mu m$ is directed upward and is perpendicular to the thin foil surface which has a reflection coefficient $\rho = 0.50$ (see the sketch of the experiment). The reflection coefficient of the surface is the ratio of the reflected energy to the incident energy. $A$ pulse with duration of $0.13 \, ms$ has a total energy of $10 \, J$. What is the mass of the piece of foil that can be supported in the air solely by the light pressure of the laser beam? (Take $g = 10 \, m/s^2$)

The radiation pressure $1 \,m$ away from a $330 \,W$ electric bulb is

Light with an average flux of $20 \, W/cm^2$ falls on a non-reflecting surface at normal incidence having a surface area of $20 \, cm^2$. The energy received by the surface during a time span of $1 \, minute$ is $............ \, J$.