The energy flux of sunlight reaching the surface of the earth is $1.388 \times 10^{3} \;W / m ^{2} .$ How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of $550\;nm$
Energy flux $=1388\, W / m^2$
wavelength $=550\, nm$
Energy of photon $=h c / \lambda$ $=3.61 \times 10^{-19} \,J$
So no. of photons $= P / E$
$=4 \times 10^{21}\; Photons / m^{2}\; s$
The work function of a metal is
Energy of photon whose frequency is ${10^{12}}MHz,$ will be
The light of two different frequencies whose photons have energies $3.8 \,eV$ and $1.4 \,eV$ respectively, illuminate a metallic surface whose work function is $0.6 \,eV$ successively. The ratio of maximum speeds of emitted electrons for the two frequencies respectivly will be
In photoelectric effect, if a weak intensity radiation instead of strong intensity of suitable frequency is used then
A pulse of light of duration $100 \ ns$ is absorbed completely by a small object initially at rest. Power of the pulse is $30 \ mV$ and the speed of light is $3 \times 10 ^8\ ms ^{-1}$. The final momentum of the object is :