List of top Physics Questions

If the emission rate of blackbody at $0^\circ\text{C}$ is $R$ then, the rate of emission at $273^\circ\text{C}$ is
For any material, if R, T and A represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then, for a blackbody which one of the following is true ?
Consider a cylindrical conductor of length $L$ and area of cross section $A$. The specific conductivity varies as $\sigma(x)=\sigma_0\frac{L}{\sqrt{x}}$ where $x$ is the distance along the axis of the cylinder from one of its ends. The resistance of the system along the cylindrical axis is
The 6 V Zener diode shown in figure has negligible resistance and a knee current of 5 mA. The minimum value of $R$ (in $\Omega$) so that the voltage across it does not fall below 6 V is
A 2 MeV neutron is emitted in a fission reactor. If it loses half of its kinetic energy in each collision with a moderator atom, how many collisions must it undergo to achieve thermal energy of 0.039 eV?
What is the minimum thickness (in nm) of a soap film ($n = 1.3$) that results in constructive interference in reflected light if the film is illuminated with light whose wavelength in free space is 620 nm?
An electron is moving with a velocity $2 \times 10^6$ m/s along positive $x$-direction in the uniform electric field of $8 \times 10^7$ V/m applied along positive $y$-direction. The magnitude and direction of a uniform magnetic field (in Tesla) that will cause the electrons to move undeviated along its original path is
The electrical conductivity of a metal is
Three point charges $4q$, $Q$ and $q$ are placed in a straight line of length $L$ at points 0, $L/2$ and $L$ respectively. The net force on charge $q$ is zero. The value of $Q$ is
A point charge $+Q$ is held at rest at a point $P$. Another point charge $-q$, whose mass is $m$, moves at a constant velocity $v$ in a circular orbit of radius $R_1$ around $P$. The work required to increase the radius of revolution of $-q$ from $R_1$ to another orbit $R_2$ is ($R_2 > R_1$)
A rectangular conducting loop of length $4\sqrt{2}$ m and breadth 4 m carrying a current of 5 A in the anti-clockwise direction is placed in the $xy$-plane. The magnitude of the magnetic induction field vector $B$ at the intersection of the diagonals is (Use $\mu_0=4\pi\times10^{-7}\,\text{NA}^{-2}$)
A particle of charge $Q$ moves with a velocity $\vec{v}=a\hat{i}$ in a magnetic field $\vec{B}=b\hat{j}+c\hat{k}$, where $a, b$ and $c$ are constants. The magnitude of the force experienced by the particle is
A voltage $V_{PQ}=V_0\cos\omega t$ is applied between the points P and Q in the network shown. $C=\frac{1}{\omega R\sqrt{3}}$ and $L=\frac{R\sqrt{3}}{\omega}$. The total impedance between P and Q is
A flat mirror revolves at a constant angular velocity making $n=0.4$ revolutions per second. With what velocity (in $\text{ms}^{-1}$) will a light spot move along a spherical screen with a radius of 15 meters, if the mirror is at the centre of curvature of the screen
A parallel beam of light of wavelength 4000 $\text{\AA}$ passes through a slit of width $5\times10^{-3}$ m. The angular spread of the central maxima in the diffraction pattern is
When two capacitors are connected in parallel the resulting combination has capacitance 10 $\mu$F. The same capacitors when connected in series results in a capacitance 0.5 $\mu$F. The respective values of individual capacitors are
A decay chain of the nucleus $^{238}_{92}\text{U}$ involves eight $\alpha$-decays and six $\beta$-decays. The final nucleus at the end of the process will be
The mean momentum of a nucleon in a nucleus with mass number A varies as
A wire made of aluminium having resistivity $\rho=2.8\times10^{-8}\,\Omega\text{ m}$ with a circular cross section and has a radius of $2\times10^{-3}$ m. A current of 5 A flows through the wire. If the voltage difference between the ends is 1 V, what is the length of the wire in meters?
Two identical systems, with heat capacity at constant volume that varies as $C_v = bT^3$ (where $b$ is a constant) are thermally isolated. Initially, one system is at a temperature 100 K and the other is at 200 K. The systems are then brought into thermal contact and the combined system is allowed to reach thermal equilibrium. The final temperature (in K) of the combined system will be
Water flows steadily through a horizontal pipe of a variable cross section. If the pressure of the water is $p$ at a point where the speed of the flow is $v$, what is the pressure at another point where the speed of the flow is $2v$; let the density of water be $\rho$
A soap bubble of radius $r$ is blown up to form a bubble of radius $2r$ under isothermal conditions. If $\sigma$ is the surface tension of soap solution, the energy spent in doing so is
The temperature of an ideal gas is increased from 100 K to 400 K. If the rms speed of the gas molecule is $v$ at 100 K then at 400 K it becomes
A uniform copper rod of 50 cm length is insulated on the sides, and has its ends exposed to ice and steam respectively. If there is a layer of water 1 mm thick at each end, the temperature gradient (in $^\circ\text{C m}^{-1}$) in the bar is (Assume that the thermal conductivity of copper is 400 $\text{W m}^{-1}\text{K}^{-1}$ and water is 0.4 $\text{W m}^{-1}\text{K}^{-1}$)
A Carnot engine whose low temperature reservoir is at 350 K has an efficiency of 50%. It is desired to increase this to 60%. If the temperature of the low temperature reservoir remains constant, then the temperature of high temperature reservoir must be increased by how many degrees?