The work function of a substance is $3.0\ \mathrm{eV}$. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately:

An important spectral emission line has a wavelength of $21 cm$. The corresponding photon energy is

$(h = 6.62 \times {10^{ – 34}}Js;\;\;c = 3 \times {10^8}m/s)$

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

If $c$ is the velocity of light in free space, the correct statements about photon among the following are:

$A$. The energy of a photon is $E=h v$.

$B$. The velocity of a photon is $c$.

$C$. The momentum of a photon, $p=\frac{h v}{c}$.

$D$. In a photon-electron collision, both total energy and total momentum are conserved.

$E$. Photon possesses positive charge.

Choose the correct answer from the options given below:

When radiation of wavelength $\lambda $ is incident on a metallic surface, the stopping potential is $4.8\, volts$. If the same surface is illuminated with radiation of double the wavelength, then the stopping potential becomes $1.6\, volts$. Then the threshold wavelength for the surface is