List of top Physics Questions

A bar AB of weight W rests like a ladder with upper end A against a smooth vertical wall and the lower end B on a rough horizontal plane. If the bar is just on the point of sliding, then the reaction at A is equal to (given that $\mu$ is coefficient of friction) :

An unstable heavy nucleus at rest breaks into two nuclei which move away with velocities in the ratio of $8 : 27$. The ratio of the radii of the nuclei (assumed to be spherical) is :

An electron , a proton and an alpha particle having the same kinetic energy are moving in circular orbits of radii $r_e, r_p, r_{\alpha} $ respectively in a uniform magnetic field $B$. The relation between $r_e, r_p, r_{\alpha}$ is :

A double inclined plane as shown in the figure has fixed horizontal base and smooth faces with the same angle of inclination of $30^{\circ}$. A block of mass $300\, g$ is on one face and is connected by a cord passing over a frictionless pulley to a second block of mass $200\, g$ kept on another face. The acceleration with which the system of the blocks moves is w.... \% of acceleration due to gravity.

Two identical non-conducting spheres having charges of -12 nC and +8 nC are touched together and then separated. The final charge on each is

The B-H curves for two ferromagnetic materials are shown in figure.

These Hysteresis loops are for

The B-H curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with 1000 turns/cm. The current that should be passed in the solenoid to demagnetise the ferromagnet completely is :

The dipole moment of a circular loop carrying a current $I$, is $m$ and the magnetic field at the centre of the loop is $B_1$. When the dipole moment is doubled by keeping the current constant, the magnetic field at the centre of the loop is $B_2$. The ratio $\frac{B_1}{B_2}$ is :

An inductor 20 mH, a capacitor 100 μF and a resistor 50Ω are connected in series across a source of emf, V = 10 sin 314 t. The power loss in the circuit is

The magnetic potential energy stored in a certain inductor is 25 mJ, when the current in the inductor is 60 mA. This inductor is of inductance

The electrostatic force between the metal plates of an isolated parallel plate capacitor C having a charge Q and area A, is

The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom, is

In a p-n junction diode, change in temperature due to heating

A set of ‘n’ equal resistors, of value ‘R’ each, are connected in series to a battery of emf ‘E’ and internal resistance ‘R’. The current drawn is I. Now, the ‘n’ resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10 I. The value of ‘n’ is

An electron of mass m with an initial velocity \(\overrightarrow{V} = V_0 \hat{i} (V_0 \gt 0)\) enters an electric field \(\overrightarrow{E} = -E_0 \;\hat{i} (E_0=constant  \gt 0)\) at t = 0. If \(\lambda_0\) is its de-Broglie wavelength initially, then its de-Broglie wavelength at time t is

In the circuit shown in the figure, the input voltage V_i is 20V, V_BE = 0 and V_CE = 0. The values of I_B , I_C and β are given by

An em wave is propagating in a medium with a velocity \(\overrightarrow{V} = V\hat{i}\) . The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along

An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be

A metallic rod of mass per unit length 0.5 kg m^-1 is lying horizontally on a smooth inclined plane which makes an angle of 30° with the horizontal. The rod is not allowed to slide down by flowing a current through it when a magnetic field of induction 0.25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is

The efficiency of an ideal heat engine working between the freezing point and boiling point of water, is

In the combination of the following gates the output Y can be written in terms of inputs A and B as

In Young’s double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same λ and D) the separation between the slits needs to be changed to

A battery consists of a variable number ‘n’ of identical cells (having internal resistance ‘r’ each) which are connected in series. The terminals of the battery are short-circuited and the current I is measured. Which of the graphs shows the correct relationship between I and n ?

A small sphere of radius ‘r’ falls from rest in a viscous liquid. As a result, heat is produced due to viscous force. The rate of production of heat when the sphere attains its terminal velocity, is proportional to

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from