Photo cells are used for the:

Assertion $(A)$: In the photoelectric effect,on increasing the intensity of light,both the number of electrons emitted and the kinetic energy of each of them increase,but the photoelectric current remains unchanged.
Reason $(R)$: The photoelectric current depends only on the wavelength of light.

Energy of an electron and a photon are equal. If the wavelength of the electron is $1\,\mathring{A}$,then the wavelength of the photon is approximately ............. $\mathring{A}$.

Two parallel discs are connected by a rigid rod of length $L=0.5 \,m$ centrally. Each disc has a slit oppositely placed as shown in the figure. $A$ beam of neutral atoms is incident on one of the discs axially at different velocities $v$,while the system is rotated at an angular speed of $600 \,rev/s$,so that atoms only with a specific velocity emerge at the other end. Calculate the two largest speeds (in $m/s$) of the atoms that will emerge at the other end.

Which of the following effects support the quantum nature of $EM$ radiation? $(1)$ Photoelectric effect $(2)$ Compton effect $(3)$ Doppler effect $(4)$ Field effect

Assertion : Photoelectric effect demonstrates the wave nature of light.
Reason : The number of photoelectrons is proportional to the frequency of light.