Modern Physics PYQ — Page 5

For a radioactive material, the half-life is $10\mathrm{minutes}$. If initially there are $600$ number of nuclei, the time taken (in $\mathrm{minutes}$) for the disintegration of $450$ nuclei 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:

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:- $(Given h=4.14\times {10}^{-15} eV s and c=3\times {10}^{8} m{ s}^{-1})$

Which one of the following represents forward bias diode?

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

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

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

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

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

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:

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:

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

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:

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)

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

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

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:

If radius of the $A1327l$ nucleus is taken to be ${R}_{Al}$ then the radius of $Te53125$ nucleus is nearly