The energy of a photon with a wavelength of $\lambda = 4000 \ \mathring{A}$ is equal to ........ Joules.

Two sources of light emit with a power of $200 \ W$. The ratio of the number of photons of visible light emitted per second by each source having wavelengths $300 \ nm$ and $500 \ nm$ respectively,will be:

The value of Planck's constant is

Write the value and unit of Planck's constant.

$A$ perfectly reflecting mirror of mass $M$ mounted on a spring constitutes a spring-mass system of angular frequency $\Omega$ such that $\frac{4 \pi M \Omega}{h} = 10^{24} \text{ m}^{-2}$,where $h$ is Planck's constant. $N$ photons of wavelength $\lambda = 8 \pi \times 10^{-6} \text{ m}$ strike the mirror simultaneously at normal incidence such that the mirror gets displaced by $1 \mu\text{m}$. If the value of $N$ is $x \times 10^{12}$,then the value of $x$ is. . . . . . . . [Consider the spring as massless]

The average number of photons emitted per second by a laser of power $6.6 \times 10^{-3} \,W$ producing light of wavelength $600 \,nm$ is (Planck's constant,$h = 6.6 \times 10^{-34} \,J \cdot s$):