Modern Physics PYQ — Page 4

A photo-emissive substance is illuminated with a radiation of wavelength $\lambda_i$ so that it releases electrons with de-Broglie wavelength $\lambda_e$. The longest wavelength of radiation that can emit photoelectron is $\lambda_0$. Expression for de-Broglie wavelength is given by : ( $\mathrm{m}:$ mass of the electron, $\mathrm{h}:$ Planck's constant and $c$ : speed of light)

Refer to the circuit diagram given in the figure. which of the following observations are correct? A. Total resistance of circuit is $6 \Omega$ B. Current in Ammeter is 1 A C. Potential across $A B$ is 4 Volts. D. Potential across CD is 4 Volts E. Total resistance of the circuit is $8 \Omega$. Choose the correct answer from the options given below: 

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: The Bohr model is applicable to hydrogen and hydrogen-like atoms only. Reason R : The formulation of Bohr model does not include repulsive force between electrons. In the light of the above statements, choose the correct answer from the options given below :

An electron in the ground state of the hydrogen atom has the orbital radius of $5.3 \times 10^{-11} \mathrm{~m}$ while that for the electron in third excited state is $8.48 \times 10^{-10} \mathrm{~m}$. The ratio of the de Broglie wavelengths of electron in the excited state to that in the ground state is

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : The density of the copper $\left({ }_{29}^{64} \mathrm{Cu}\right)$ nucleus is greater than that of the carbon $\left({ }_6^{12} \mathrm{C}\right)$ nucleus. Reason (R): The nucleus of mass number A has a radius proportional to $\mathrm{A}^{1 / 3}$. In the light of the above statements, choose the most appropriate answer from the options given below :

For a nucleus of mass number $A$ and radius $R$, the mass density of nucleus can be represented as

Considering the Bohr model of hydrogen like atoms, the ratio of the ratio of the radius $5^{\text {th }}$ orbit of the electron in $\mathrm{Li}^{2+}$ and $\mathrm{He}^{+}$is

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason $\mathrm{R}$ Assertion A: In photoelectric effect, on increasing the intensity of incident light the stopping potential increases. Reason R : Increase in intensity of light increases the rate of photoelectrons emitted, provided the frequency of incident light is greater than threshold frequency. In the light of the above statements, choose the correct answer from the options given below

Match the LIST-I with LIST-II $\begin{array}{|l|l|l|l|}\hline & \text{LIST-I} & & \text{LIST-II} \\ \hline \text{A.} & \begin{array}{l} { }_0^1 \mathrm{n}+{ }_{92}^{235} \mathrm{U} \\ \rightarrow{ }_{54}^{140} \mathrm{Xe}+{ }_{38}^{94} \mathrm{Sr}+2{ }_0^1 \mathrm{n} \end{array} & \text{I.} & \begin{array}{l} \text{Chemical} \\ \text{reaction} \end{array} \\ \hline \text{B.} & 2 \mathrm{H}_2+\mathrm{O}_2 \rightarrow 2 \mathrm{H}_2 \mathrm{O} & \text{II.} & \begin{array}{l} \text{Fusion} \\ \text{with +ve} \\ \text{Q value} \end{array} \\ \hline \text{C.} & { }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} \rightarrow{ }_2^3 \mathrm{He}+{ }_0^1 \mathrm{n} & \text{III.} & \text{Fission} \\ \hline \text{D.} & { }_1^1 \mathrm{H}+{ }_1^3 \mathrm{H} \rightarrow{ }_1^2 \mathrm{H}+{ }_1^2 \mathrm{H} & \text{IV.} & \begin{array}{l} \text{Fusion} \\ \text{with -ve Q} \\ \text{value} \end{array} \\ \hline\end{array}$ Choose the correct answer from the options given below :

In photoelectric effect an em-wave is incident on a metal surface and electrons are ejected from the surface. If the work function of the metal is 2.14 eV and stopping potential is 2 V , what is the wavelength of the em-wave ? (Given hc $=1242 \mathrm{eVnm}$ where h is the Planck's constant and c is the speed of light in vaccum.)

The output voltage in the following circuit is (Consider ideal diode case) 

Assuming the validity of Bohr's atomic model for hydrogen like ions the radius of $\mathrm{Li}^{++}$ion in its ground state is given by $\frac{1}{X} a_0$, where $X=$ _______. (Where $\mathrm{a}_0$ is the first Bohr's radius.)

 In the circuit shown here, assuming threshold voltage of diode is negligibly small, then voltage $V_{A B}$ is correctly represented by :

The work functions of cesium (Cs) and lithium (Li) metals are 1.9 eV and 2.5 eV , respectively. If we incident a light of wavelength 550 nm on these two metal surfaces, then photo-electric effect is possible for the case of

Which of the following circuits has the same outpur as that of the given circuit? 

 \begin{array}{c|c|c} A & B & Y \\\hline 0 & 0 & 1 \\0 & 1 & 1 \\1 & 0 & 0 \\1 & 1 & 1\end{array} To obtain the given truth table, following logic gate should be placed at G:

The work function of a metal is 3 eV. The color of the visible light that is required to cause emission of photoelectrons is

In the digital circuit shown in the figure, for the given inputs the P and Q values are : 

In a hydrogen like ion, the energy difference between the $2^{\text {nd }}$ excitation energy state and ground is 108.8 eV. The atomic number of the ion is

A radioactive material P first decays into Q and then Q decays to non-radioactive material R. Which of the following figure represents time dependent mass of $\mathrm{P}, \mathrm{Q}$ and R ?

The output of the circuit is low (zero) for :  (A) $\mathrm{X}=0, \mathrm{Y}=0$ (B) $X=0, Y=1$ (C) $X=1, Y=0$ (D) $\mathrm{X}=1, \mathrm{Y}=1$ Choose the correct answer from the options given below :

The Boolean expression $\mathrm{Y}=\mathrm{A} \overline{\mathrm{B}} \mathrm{C}+\overline{\mathrm{A}} \overline{\mathrm{C}}$ can be realised with which of the following gate configurations. A. One 3-input AND gate, 3 NOT gates and one 2input OR gate, One 2-input AND gate, B. One 3-input AND gate, 1 NOT gate, One 2input NOR gate and one 2-input OR gate C. 3-input OR gate, 3 NOT gates and one 2-input AND gate Choose the correct answer from the options given below

The de Broglie wavelength of a particle with mass m and velocity v is:

A zener diode with 5 V zener voltage is used to regulate an unregulated dc voltage input of 25 V. For a $400 \Omega$ resistor connected in series, the zener current is found to be 4 times load current. The load current $\left(I_L\right)$ and load resistance $\left(R_{\mathrm{L}}\right)$ are :