Sodium and copper have work functions of $2.3 \ eV$ and $4.5 \ eV$ respectively. The ratio of their threshold wavelengths is approximately .......

The photoelectric work function for a metal surface is $4.125 \ eV$. The cut-off wavelength for this surface is .......... $\mathring{A}$.

Find the number of electrons emitted per second by a $24 \, W$ source of monochromatic light of wavelength $6600 \, \mathring{A}$, assuming $3 \%$ efficiency for the photoelectric effect (take $h = 6.6 \times 10^{-34} \, J \cdot s$ and $c = 3 \times 10^8 \, m/s$).

In a photoelectric experiment,electrons are ejected from metals $X$ and $Y$ by light of intensity $I$ and frequency $f$. The potential difference $V$ required to stop the electrons is measured for various frequencies. If $Y$ has a greater work function than $X$,which one of the following graphs best illustrates the expected results?

Electrons are emitted with kinetic energy $T$ from a metal plate by an irradiation of light of intensity $J$ and frequency $v$. Then,which of the following will be true?

The light of wavelength $\lambda$ is incident on the surface of a metal with work function $\phi$ and emits electrons. What is the maximum velocity of the emitted electrons? [Given: $m=$ mass of electron,$h=$ Planck's constant,$c=$ velocity of light]