Modern Physics PYQ — Page 5

The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom is

The ratio of wavelengths of the last line of the Balmer series and the last line of the Lyman series is_____.

Radioactive material $A$ has decay constant $8\lambda$ and material $B$ has decay constant $\lambda$. Initially they have the same number of nuclei. After what time, the ratio of number of nuclei of material $A$ to that $B$ will be $\frac{1}{e}?$

The given electrical network is equivalent to 

The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature $T$ (Kelvin) and mass $m$ is:

Which one of the following represents forward bias diode?

The photoelectric threshold wavelength of silver is $3250\times {10}^{–10} m$. The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength $2536\times {10}^{–10} m$ is:- $(Given h=4.14\times {10}^{-15} eV s and c=3\times {10}^{8} m{ s}^{-1})$

Given the value of Rydberg constant is ${10}^{7} {m}^{-1}$, the wave number of the last line of the Balmer series in hydrogen spectrum will be:

The given circuit has two ideal diodes connected as shown in the figure below. The current flowing through the resistance ${R}_{1}$ will be 

Photons with energy of $5\mathrm{eV}$ are incident on a cathode, $C$ in a photoelectric cell. The maximum energy of emitted photoelectrons is $2 eV.$ When photons of energy $6eV$ are incident on $C$, no photoelectrons will reach the anode, $A$, if, the stopping potential of $A$ relative to $C$ is

If an electron in a hydrogen atom jumps from the third orbit to the second orbit, it emits a photon of wavelength $\lambda$. When it jumps from the fourth orbit to the third orbit, the corresponding wavelength of the photon will be

Consider the junction diode as ideal. The value of current flowing through AB is: 

When a metallic surface is illuminated with radiation of wavelength $\lambda$, the stopping potential is $V$. If the same surface is illuminated with radiation of wavelength $2\lambda$, the stopping potential is $\frac{V}{4}$. The threshold wavelength for the metallic surface is:

What is the output $Y$ in the following circuit, when, all the three inputs $A, B, C$ are first $0$ and then, $1$? 

To get output $1$ for the following circuit, the correct choice for the input is: 

The half-life of a radioactive substance is $30\mathrm{min}$. The time (in minutes) taken between $40%$ decay and $85%$ decay of the same radioactive substance is

When an $\alpha$ -particle of mass $m$ moving with a undefined velocity bombards on a heavy nucleus of charge $\mathrm{Ze}$, its distance of the closest approach from the nucleus depends on $m$ as:

Electrons of mass, $m$ with de-Broglie wavelength, $\lambda$ fall on the target in an X-ray tube. The cutoff wavelength, $({\lambda }_{0})$ of the emitted X-ray is

An electron of mass m and a photon have same energy $E.$ The ratio of de-Broglie wavelengths associated with them is: ($c$ being velocity of light)

Light of wavelength $500\mathrm{nm}$ is incident on a metal with work function $2.28\mathrm{eV}$. The de Broglie wavelength of the emitted electron is:

The input signal is given to a CE amplifier having a voltage gain of $150$ is ${V}_{i}=2\mathrm{cos}⁡(15t+\frac{\pi }{3})$. The corresponding output signal will be:

In the given figure, a diode $D$ is connected to an external resistance $R=100\Omega$ and an $emf$ of $3.5V$ If the barrier potential developed across the diode is $0.5V$, the current in the circuit will be 

A nucleus of uranium decays at rest into nuclei of thorium and helium. Then:

When a certain metallic surface is illuminated with monochromatic light of wavelength $\lambda ,$ the stopping potential for photoelectric current is $3{V}_{0}$ and when the same surface is illuminated with light of wavelength $2\lambda ,$ the stopping potential is ${V}_{0}.$ The threshold wavelength of this surface for photoelectric effect is