NEET UG 2012 — Modern Physics

A $200 \mathrm{~W}$ sodium street lamp emits yellow light of wavelength $0.6 \mu \mathrm{m}$. Assuming it to be $25 \%$ efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

An $\alpha$-particle moves in a circular path of radius $0.83 \mathrm{~cm}$ in the presence of a magnetic field of $0.25 \mathrm{~Wb} / \mathrm{m}^2$. The de-Broglie wavelength associated with the particle will be

An electron of a stationary hydrogen atom passes from the fifth energy level to the ground level. The velocity that the atom acquired as a result of photon emission will be ( $m$ is the mass of the electron, $R$ Rydberg constant and $h$ Planck's constant)

Two radiations of photon energies $1 \mathrm{eV}$ and $2.5 \mathrm{eV}$, successively illuminate a photosensitive metallic surface of work function $0.5 \mathrm{eV}$. The ratio of the maximum speeds of the emitted electrons is

The transition from the state $n=3$ to $n=1$ in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from

The half life of a radioactive nucleus is 50 days. The time interval $\left(t_2-t_1\right)$ between the time $t_2$ when $\frac{2}{3}$ of it has decayed and the time $t_1$ when $\frac{1}{3}$ of it had decayed is

If the momentum of an electron is changed by $p$, then the de-Broglie wavelength associated with it changes by $0.5 \%$. The initial momentum of electron will be

To get an output $Y=1$ in given circuit which of the following input will be correct 

A mixture consists of two radioactive materials $A_1$ and $A_2$ with half lives of $20 \mathrm{~s}$ and $10 \mathrm{~s}$ respectively. Initially the mixture has $40 \mathrm{~g}$ of $A_1$ and $160 \mathrm{~g}$ of $A_2$. The amount of the two in the mixture will become equal after

The figure shows a logic circuit with two inputs $A$ and $B$ and the output $C$. The voltage wave forms across $A, B$ and $C$ are as given. The logic circuit gate is 

Two ideal diodes are connected to a battery as shown in the circuit. The current supplied by the battery is 

If the nuclear radius of ${ }^{27} \mathrm{Al}$ is $3.6 \mathrm{Fermi}$, the approximate nuclear radius of ${ }^{64} \mathrm{Cu}$ in Fermi is

$C$ and Si both have same lattice structure, having 4 bonding electrons in each. However, $C$ is insulator whereas $\mathrm{Si}$ is intrinsic semiconductor. This is because

Electron in hydrogen atom first jumps from third excited state to second excited state and then from second excited to the first excited state. The ratio of the wavelengths $\lambda_1: \lambda_2$ emitted in the two cases is

Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be $3.57 \mathrm{~V}$. The threshold frequency of the material is