The particle having zero rest mass is

Specific heat of water is $4.2 \, J/g^{\circ}C$. If light of frequency $3 \times 10^9 \, Hz$ is used to heat $400 \, g$ of water from $20^{\circ}C$ to $40^{\circ}C$,the number of photons needed will be:

When light of wavelength $\lambda$ is incident on a photosensitive surface,photons of power $P$ are emitted. The number of photons $n$ emitted in time $t$ is: [$h$ = Planck's constant,$c$ = velocity of light in vacuum]

The photon energy in units of $eV$ for an electromagnetic wave of wavelength $2 \, cm$ is

An electron and a photon have the same wavelength of $10^{-9} \, m$. If $E$ is the energy of the photon and $p$ is the momentum of the electron,then the magnitude of $E / p$ (in $SI$ unit) is

The number of photons of wavelength $540 \ nm$ emitted per second by an electric bulb of power $100 \ W$ is (taking $h = 6 \times 10^{-34} \ J \cdot s$ and $c = 3 \times 10^8 \ m/s$):