Modern Physics PYQ — Page 8

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

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

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

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?

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

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

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 forward biasing of the $p-n$ junction

If a small amount of antimony is added to germanium crystal

Fusion reaction takes place at high temperature because

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

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 

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

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

Which one of the following statement is false?

When monochromatic radiation of intensity $I$ falls on a metal surface, the number of photoelectron and their maximum kinetic energy are $N$ and $T$ respectively. If the intensity of radiation is 2I, the number of emitted electrons and their maximum kinetic energy are respectively

To get an output $Y=1$ from the circuit shown below, the input must be  

The potential difference that must be applied to stop the fastest photoelectrons emitted by a nickel surface, having work function $5.01 \mathrm{eV}$, when ultraviolet light of $200 \mathrm{~nm}$ falls on it, must be

The mass of a ${ }_3 \mathrm{Li}^7$ nucleus is $0.042 \mathrm{u}$ less than the sum of the masses of all its nucleons. The binding energy per nucleon of ${ }_3 \mathrm{Li}^7$ nucleus is nearly

The following figure shows a logic gate circuit with two inputs $A$ and $B$ and the output $Y$. The voltage waveforms of $A, B$ and $Y$ are as given   The logic gate is

The energy of a hydrogen atom in the ground state is $-13.6 \mathrm{eV}$. The energy of a $\mathrm{He}^{+}$ion in the first excited state will be

The electron in the hydrogen atom jumps from excited state $(n=3)$ to its ground state $(n=1)$ and the photons thus emitted irradiate a photosensitive material. If the work function of the material is $5.1 \mathrm{eV}$, the stopping potential is estimated to be (the energy of the electron in $n$th state $\mathrm{E}_{\mathrm{n}}=-\frac{13.6}{\mathrm{n}^2} \mathrm{eV}$ )

The device that can act as a complete electronic circuit is