Modern Physics PYQ — Page 4

The half life of radioactive sample undergoing $\alpha$-decay is $1.4\times {10}^{17}s.$ If the number of nuclei in the sample is $2.0\times {10}^{21},$ the activity of the sample is nearly:

Light of frequency $1.5$ times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled?

The energy equivalent of $0.5g$ of a substance is:

An electron is accelerated from rest through a potential difference of $V$ volt. If the de Broglie wavelength of the electron is $1.227\times {10}^{–2} \mathrm{nm}$, the potential difference is:

The solids which have the negative temperature coefficient of resistance are:

For which one of the following, Bohr model is not valid?

For a $p-$type semiconductor, which of the following statements is true?

The circuit diagram shown here corresponds to the logic gate, 

The binding energy per nucleon is maximum for

An electron is accelerated through a potential difference of $10,000 V.$ Its de Broglie wavelength is (nearly): $({m}_{e}=9\times 1{0}^{-31} kg)$

An LED is constructed from a p-n junction diode using GaAsP. The energy gap is $1.9 \mathrm{eV}$. The wavelength of the light emitted will be equal to

$\text{α}$-particle consists of

The correct Boolean operation represented by the circuit diagram drawn is, 

The rate of radioactive disintegration at an instant for a radioactive sample of half life $2.2 \times 10^9 \mathrm{~s}$ is $10^{10} \mathrm{~s}^{-1}$. The number of radioactive atoms in that sample at that instant is

The total energy of an electron in an atom in an orbit is $-3.4 eV.$ Its kinetic and potential energies are, respectively,

The work function of a photosensitive material is $4.0 \mathrm{eV}$. This longest wavelength of light that can cause photon emission from the substance is (approximately)

The radius of the first permitted Bohr orbit for the electron, in a hydrogen atom equals $0.51 Å$ and its ground state energy equals $-13.6 \mathrm{eV}$. If the electron in the hydrogen atom is replaced by muon $\left(\mu^{-1}\right)$ [Charge same as electron and mass $207 \mathrm{~m}_{\mathrm{e}}$ ], the first Bohr radius and ground state energy will be

A proton and an $\alpha$-particle are accelerated from rest to the same energy. The de-Broglie wavelengths $\lambda_p$ and $\lambda_\alpha$ are in the ratio

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

In the combination of the following gates the output $Y$ can be written in terms of inputs $A$ and $B$ as 

In a $p-n$ junction diode, change in temperature due to heating

In the circuit shown in the figure, the input voltage ${V}_{i} \text{is} 20 V, {V}_{BE}=0 \text{and} {V}_{CE}=0$. The values of ${I}_{B},{I}_{C} \text{and} \beta$ are given by 

An electron of mass $m$ with an initial velocity $\vec{V}={V}_{0} \hat{i} ({V}_{0}>0)$ enters in an electric field $\vec{E}={-E}_{0}\hat{i}({E}_{0}>0$ and is a constant$)$ at $t=0$. If ${\lambda }_{0}$ is its de-Broglie wavelength initially, then its de-Broglie wavelength at time $t$ is

When the light of frequency $2{\nu }_{0}$ (where ${\nu }_{0}$ is threshold frequency), is incident on a metal plate, the maximum velocity of electrons emitted is ${v}_{1}$. When the frequency of the incident radiation is increased to $5{\nu }_{0},$ the maximum velocity of electrons emitted from the same plate is ${v}_{2}.$ The ratio of ${v}_{1} to {v}_{2}$ is