The momentum of a photon of light of frequency $f$ is . . . . . . .

The momentum of a photon with frequency $1.5 \times 10^{13} \ Hz$ is .......

$A$ transmitter of power $10 \text{ kW}$ emits radio waves of wavelength $500 \text{ m}$. The number of photons emitted per second by the transmitter is of the order of:

$A$ 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?

The eye can detect $5 \times 10^4$ photons per square metre per second of green light $(\lambda = 5000 \ \mathring{A})$ while the ear can detect $10^{-13} \ W/m^2$. The factor by which the eye is more sensitive as a power detector than the ear is close to:

An electron with rest mass $m_{0}$ moves with a speed of $0.8 c$. Its mass when it moves with this speed is