NEET UG 2011 — Modern Physics

A nucleus ${ }_n^m X$ emits one $\alpha$-particle and two $\beta^{-}$particles. The resulting nucleus is

A radioactive nucleus of mass $M$ emits a photon of frequency $v$ and the nucleus recoils. The recoil energy will be

A transistor is operated in common emitter configuration at $V_C=2 \mathrm{~V}$ such that a change in the base current from $100 \mu \mathrm{A}$ to $300 \mu \mathrm{A}$ produces a change in the collector current from $10 \mathrm{~mA}$ to $20 \mathrm{~mA}$. The current gain is

A zener diode, having breakdown voltage equal to $15 \mathrm{~V}$, is used in a voltage regulator circuit shown in figure. The current through the diode is 

Electrons used in an electron microscope are accelerated by a voltage of $25 \mathrm{kV}$. If the voltage is increased to $100 \mathrm{kV}$ then the de-Broglie wavelength associated with the electrons would

Fusion reaction takes place at high temperature because

If a small amount of antimony is added to germanium crystal

In forward biasing of the $p-n$ junction

In photoelectric emission process from a metal of work function $1.8 \mathrm{eV}$, the kinetic energy of most energetic electrons is $0.5 \mathrm{eV}$. The corresponding stopping potential is

In the following figure, the diodes which are forward biased, are A.  B. C. D.

Light of two different frequencies whose photons have energies $1 \mathrm{eV}$ and $2.5 \mathrm{eV}$ respectively illuminate a metallic surface whose work function is $0.5 \mathrm{eV}$ successively. Ratio of maximum speeds of emitted electrons will be

Out of the following which one is not a possible energy for a photon to be emitted by hydrogen atom according to Bohr's atomic model?

Photoelectric emission occurs only when the incident light has more than a certain minimum

Pure Si at $500 \mathrm{~K}$ has equal number of electron $\left(n_e\right)$ and hole $\left(n_h\right)$ concentrations of $1.5 \times 10^{16} \mathrm{~m}^{-3}$. Doping by indium increases $n_h$ to $4.5 \times 10^{22} \mathrm{~m}^{-3}$. The doped semiconductor is of

Symbolic representation of four logic gates are shown as     Pick out which ones are for AND, NAND and NOT gates, respectively.

The half-life of a radioactive isotope $X$ is $50 \mathrm{yr}$. It decays to another element $Y$ which is stable. The two elements $X$ and $Y$ were found to be in the ratio of $1: 15$ in a sample of a given rock. The age of the rock was estimated to be

The power obtained in a reactor using $\mathrm{U}^{235}$ disintegration is $1000 \mathrm{~kW}$. The mass decay of $\mathrm{U}^{235}$ per hour is

The threshold frequency for a photo-sensitive metal is $3.3 \times 10^{14} \mathrm{~Hz}$. If light of frequency $8.2 \times 10^{14} \mathrm{~Hz}$ is incident on this metal, the cut-off voltage for the photo-electric emission is nearly

The wavelength of the first line of Lyman series for hydrogen atom is equal to that of the second line of Balmer series for a hydrogen like ion. The atomic number $Z$ of hydrogen like ion is

Two radioactive nuclei $P$ and $Q$, in a given sample decay into a stable nucleous $R$. At time $t=0$, number of $P$ species are $4 N_0$ and that of $Q$ are $N_0$. Half-life of $P$ (for conversion to $R$ ) is 1 min where as that of $Q$ is $2 \mathrm{~min}$. Initially there are no nuclei of $R$ present in the sample. When number of nuclei of $P$ and $Q$ are equal, the number of nuclei of $R$ present in the sample would be