Modern Physics - Physics Previous Year Questions

Consider the circuit with a Zener diode whose breakdown voltage $V_z=4 \mathrm{~V}$. What is the voltage $V_0$ if $V_i=20 \mathrm{~V}$ ?

Two monochromatic sources emit light at wavelengths $\lambda$ and $\lambda / 2$. The stopping potentials for a photosensitive material using these two sources are found to be 1 V and 3 V , respectively. What is the work function of the material?

An electron in the ground state (with energy $E_1$ ) of a hydrogen atom, absorbs a photon of energy $E_a$, and gets excited to a higher energy level of principal quantum number $n$. What is the value of $n$ ?

An electron of mass $m_e$ has a speed $u_n$ in the $n^{\text {th }}$ Bohr orbit of a hydrogen atom. The normalized speed $V_n$ is given as $V_n=u_n / c=1 / 685$ and the mass of the electron in the units of energy is given as $M_e=m_e c^2=0.51 \times 10^6 \mathrm{eV}$, where $c$ is the velocity of light in a vacuum. It is given that $\frac{e^2}{2 \epsilon_0 h c}=1 / 137$. The Planck's constant h is given as $4.13 \times 10^{-15} \mathrm{eV}-\mathrm{sec}$. The electron makes a transition from $n^{\text {th }}$ orbit to the ground state of the atom. What is the frequency of the emitted photon?