What is a photon?

The frequency of a photon having energy $100 \ eV$ is $(h = 6.6 \times 10^{-34} \ J \cdot s)$.

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 $550 \; nm$.

$A$ bulb lamp emits light of mean wavelength of $4500 \mathring A$. The lamp is rated at $150 \text{ W}$ and $8 \%$ of the energy appears as emitted light. How many photons are emitted by the lamp per second?

$A$ transmitter of $100 \ W$ power emits electromagnetic waves of wavelength $540 \ nm$. How many photons are emitted per second? (Given: $h = 6 \times 10^{-34} \ J \cdot s$,$c = 3 \times 10^8 \ m/s$)

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: