The number of photons emitted from a photocell by a source placed at a distance of $0.5 \ m$ is how many times the number of photons emitted by the same source placed at a distance of $1 \ m$?

There are two sources of light,each emitting with a power of $100 \, W$. One emits $X$-rays of wavelength $1 \, nm$ and the other visible light at $500 \, nm$. Find the ratio of the number of photons of $X$-rays to the photons of visible light of the given wavelength.

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: $h = 6.63 \times 10^{-34} \,Js$,$c = 3 \times 10^8 \,m/s$)

There are $n_1$ photons of frequency $\nu_1$ in a beam of light. In an equally energetic beam,there are $n_2$ photons of frequency $\nu_2$. Then the correct relation is

Assertion: The energy $(E)$ and momentum $(p)$ of a photon are related by $p = E/c$.
Reason: The photon behaves like a particle.

The momentum of a photon of wavelength $\lambda$ is