List of top Physics Questions

Consider two Carnot engines of efficiencies $\eta_1$ and $\eta_2$. The first engine absorbs heat $Q_1$ from a heat reservoir A and releases heat $Q_2$ to a heat reservoir B. The second engine takes heat $Q_2$ from B and releases heat $Q_3$ to a heat reservoir C. If $Q_1 > Q_2 > Q_3$, what is the net efficiency of this combination of the two Carnot engines?

A jar is filled with two monoatomic non-interacting gases A and B with total masses $M_A$ and $M_B$, respectively. The molar mass of A is double the molar mass of B. If the jar is kept at temperature $T$, what is the ratio of the total pressure of the combined gas to the partial pressure due to the gas A?

The three numbers: (number of protons, number of neutrons, the radius) characterize a nucleus. What is the value of $\frac{r_1}{r_2}$ for two nuclei characterized by $(1, 0, r_1)$ and $(4, 4, r_2)$?

An experimental study of the photoelectric effect involves a metal of work function $\phi_0$. What is the smallest wavelength of the incident photon to photoemit an electron of mass $m$ which has the same de Broglie wavelength as that of the incident photon? [Given $h$ is the Planck's constant, $c$ is the speed of light, and $\phi_0 \ll mc^2$]

Consider normal incidence of a monochromatic beam of photons of power $P$ on a flat surface. Of the incident beam, 10% gets absorbed, 10% gets transmitted, and the rest is reflected by the flat surface. If $c$ is the speed of light, what is the force exerted on the flat surface by the beam?

The acceleration of a point particle is given by the equation \[ \frac{d^2\mathbf{x}}{dt^2} = \alpha \frac{\mathbf{x}}{|\mathbf{x}|^7} + \beta \frac{d\mathbf{x}}{dt} \] where $\mathbf{x}$ denotes position and $t$ denotes time. Which of the following relations show the correct dimensions for $\alpha$ and $\beta$?

A long solenoid of initial radius $R_0$ is put in a region of uniform magnetic field $\mathbf{B}$ with the axis of the solenoid aligned along the magnetic field. The solenoid is a part of a closed circuit that has no initial current running through it. If the radius of the solenoid starts increasing at a uniform rate, how do the magnetic field strength $B_{in}$ and the associated magnetic energy $U_{in}$ inside the solenoid change?

The position of a particle of mass 1 kg at time $t$ is given by $\mathbf{r} = t\hat{i} + \hat{j} + 2t^2\hat{k}$, where $t$ is in seconds and the coefficients have the proper units for $\mathbf{r}$ to be in metres. What is the component of the angular momentum (with respect to the origin) in kg m$^2$ s$^{-1}$ along the vector $(\hat{i} + \hat{j})$?

A planet is revolving in a circular orbit with a time period $T$ around the center of a star solely under the gravity of the star. Suppose the distance between the star and the planet is halved. The individual radii of the star and the planet are also halved, keeping their uniform mass densities unchanged. What will be the time period of the new orbit of the planet?

An exotic spherical jellyfish has a bulk modulus $B$. Close to the surface of the sea (depth $d=0$), its radius is $R$. When it dives to a depth $d$ ($d \gg R$), its radius is reduced by $\Delta R > 0$. Given the density of the incompressible sea water $\rho$, and the uniform acceleration due to gravity $g$ such that $\rho g d \ll B$, what is $\frac{\Delta R}{R}$?

A particle of mass $m_1$ and electric charge $q$ starts from rest under the influence of a uniform external electric field $\mathbf{E}$ to travel a distance $d$ in time $t_1$. If the particle had mass $m_2$, it would take time $t_2$ to travel the same distance. What is the ratio $\frac{t_1}{t_2}$?

A simple pendulum of length $L$, mass $m$ and electric charge $q$ on its bob is oscillating with a time period $T$ under uniform gravity which is in the $-\hat{z}$ direction. Upon applying a uniform electric field $|E|\hat{n}$ (where $\hat{n}$ is a unit vector in the plane of oscillation), the time period of the pendulum decreases. Which of the following statements is NOT correct?

Two forces of 4 N and 3 N act on a particle. For maximum resultant force, the angle between them should be-

In a tube, a liquid is flowing as shown in the diagram. The correct order of the velocity (u) of liquid flowing in this tube is: figure [H]

figure

Over modulation occurs when modulation index 'm' is:

If decay constant of a radioactive element doubles, then its half-life time becomes:

If the average energy density of the electric field of an electromagnetic wave is $U_E$ and the average energy density of the magnetic field of the wave is $U_B$, then:

A resistor of resistance 30 $\Omega$ and a capacitor of reactance 40 $\Omega$ are connected in series to an ac supply. If the rms current through the resistor is 2 mA, then the wattless current is:

For the circuit given below, which of the following is correct option?

In hydrogen atom, if the kinetic energy of an electron in an orbit having angular momentum $2h/\pi$ is E, then the potential energy of the electron in the first orbit of hydrogen atom is:

The energy of a photon of wavelength 2500 is 4.96 eV. When photons of wavelength 3100 incident on a photosensitive material of work function 2.2 eV, the maximum velocity of the emitted photoelectrons is:

If a straight infinitely long horizontal wire carries a current of 50 A in east-west direction, then the magnitude of the magnetic field due to the current at a vertical distance of 2 m above the wire is: