JEE Main Physics — Modern Physics previous year questions with solutions.
The de Broglie wavelength of a particle with mass m and velocity v is:
If \(\lambda\) and \(K\) are de Broglie wavelength and kinetic energy, respectively, of a particle with constant mass. The correct graphical representation for the particle will be
The energy $E$ and momentum $p$ of a moving body of mass $m$ are related by some equation. Given that c represents the speed of light, identify the correct equation
The work function of a metal is 4.2 eV. What is the threshold wavelength for photoelectric emission? (hc = 1240 eV·nm)
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)
In photoelectric effect, the stopping potential $\left(\mathrm{V}_0\right) \mathrm{v} / \mathrm{s}$ frequency $(\nu)$ curve is plotted. ( h is the Planck's constant and $\phi_0$ is work function of metal ) (A) $\mathrm{V}_0 \mathrm{v} / \mathrm{s} \nu$ is linear. (B) The slope of $\mathrm{V}_0 \mathrm{v} / \mathrm{s} \nu$ curve $=\frac{\phi_0}{\mathrm{~h}}$ (C) h constant is related to the slope of $\mathrm{V}_0 \mathrm{v} / \mathrm{s} \nu$ line. (D) The value of electric charge of electron is not required to determine $h$ using the $V_0 \mathrm{v} / \mathrm{s} \nu$ curve. (E) The work function can be estimated without knowing the value of $h$. 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.)
A monochromatic light is incident on a metallic plate having work function $\phi$. An electron, emitted normally to the plate from a point $A$ with maximum kinetic energy, enters a constant magnetic field, perpendicular to the initial velocity of electron. The electron passes through a curve and hits back the plate at a point $B$. The distance between A and B is : (Given : The magnitude of charge of an electron is e and mass is $\mathrm{m}, \mathrm{h}$ is Planck's constant and c is velocity of light. Take the magnetic field exists throughout the path of electron)
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
Choose the correct logic circuit for the given truth table having inputs A and B. $\begin{array}{|c|c|c|} \hline \text{Inputs} & & \text{Output} \\ \hline A & B & Y \\ \hline 0 & 0 & 0 \\ \hline 0 & 1 & 0 \\ \hline 1 & 0 & 1 \\ \hline 1 & 1 & 1 \\ \hline \end{array}$
Consider the following statements: A. The junction area of solar cell is made very narrow compared to a photo diode. B. Solar cells are not connected with any external bias. C. LED is made of lightly doped p-n junction. D. Increase of forward current results in continuous increase of LED light intensity. E. LEDs have to be connected in forward bias for emission of light. Choose the correct answer from the options given below:
Considering Bohr's atomic model for hydrogen atom : (A) the energy of H atom in ground state is same as energy of $\mathrm{He}^{+}$ion in its first excited state. (B) the energy of H atom in ground state is same as that for $\mathrm{Li}^{++}$ion in its second excited state. (C) the energy of H atom in its ground state is same as that of $\mathrm{He}^{+}$ion for its ground state. (D) the energy of $\mathrm{He}^{+}$ion in its first excited state is same as that for $\mathrm{Li}^{++}$ion in its ground state Choose the correct answer from the options given below :
Choose the correct nuclear process from the below options [p: proton, n : neutron, $\mathrm{e}^{-}$: electron, $\mathrm{e}^{+}$: positron, $v:$ neutrino, $\bar{v}$ : antineutrino]
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 :
A proton of mass ' $m_{\mathrm{p}}$ ' has same energy as that of a photon of wavelength ' $\lambda$ '. If the proton is moving at non-relativistic speed, then ratio of its de Broglie wavelength to the wavelength of photon is.
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Emission of electrons in photoelectric effect can be suppressed by applying a sufficiently negative electron potential to the photoemissive substance. Reason (R) : A negative electric potential, which stops the emission of electrons from the surface of a photoemissive substance, varies linearly with frequency of incident radiation. In the light of the above statements, choose the most appropriate answer from the options given below :
In the following circuit, the reading of the ammeter will be (Take Zener breakdown voltage $=4 \mathrm{~V})$ 
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: 
In an experiment with photoelectric effect, the stopping potential,
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 :
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 :
Consider the following logic circuit.  The output is $\mathrm{Y}=0$ when :
For a nucleus of mass number $A$ and radius $R$, the mass density of nucleus can be represented as
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