Write equation of mass of photon. 

Light of intensity $10^{-5}\; W m ^{-2}$ falls on a sodium photo-cell of surface area $2 \;cm ^{2}$. Assuming that the top $5$ layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave-picture of radiation. The work function for the metal is given to be about $ 2\; eV$. What is the implication of your answer?

Photo cells are used for the

If $2.5 \times 10^{-6\,} N$ average force is exerted by a light wave on a non-reflecting surface of $30\, cm ^{2}$ area during $40$ minutes of time span, the energy flux of light just before it falls on the surface is .................. $W / cm ^{2}$

(Round off to the Nearest Integer)

(Assume complete absorption and normal incidence conditions are there)

Consider figure for photoemission.

How would you reconcile with momentum-conservation ? Note light (photons) have momentum in a different direction than the emitted electrons. 

If $c$ is the velocity of light in free space, the correct statements about photon among the following are:

$A$. The energy of a photon is $E=h v$.

$B$. The velocity of a photon is $c$.

$C$. The momentum of a photon, $p=\frac{h v}{c}$.

$D$. In a photon-electron collision, both total energy and total momentum are conserved.

$E$. Photon possesses positive charge.

Choose the correct answer from the options given below: