The particle having zero rest mass is

What is the energy and momentum of a photon having frequency $v$?

Monochromatic light of wavelength $667 \, nm$ is produced by a helium-neon laser. The power emitted is $9 \, mW$. The number of photons arriving per second on average at a target irradiated by this beam is:

The radiant energy from the Sun incident on the Earth's surface is $2 \ cal/cm^2 \cdot min$. If the average wavelength of solar radiation is $5500 \ \mathring A$,then the number of photons incident per minute on a surface area of $1 \ cm^2$ on the Earth's surface is ............ $(h = 6.6 \times 10^{-34} \ J \cdot s, 1 \ cal = 4.2 \ J)$

How many photons are emitted by a laser source of $5 \times 10^{-3} \,W$ operating at $632.2 \,nm$ in $2 \,s$? The answer is $....... \times 10^{16}$. (Given: $h = 6.63 \times 10^{-34} \,Js$,$c = 3 \times 10^8 \,m/s$)

$A$ sensor is exposed for time $t$ to a lamp of power $P$ placed at a distance $l$. The sensor has a circular opening that is $4d$ in diameter. Assuming all energy of the lamp is given off as light,the number of photons entering the sensor if the wavelength of light is $\lambda$ is (given $l >> d$):