List of top Physics Questions

Draw the circuit diagram of a Wheatstone bridge. Obtain the condition when no current flows through the galvanometer in it.
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% Wheatstone Bridge Diagram Explanation Circuit Diagram and Condition:
The Wheatstone bridge consists of a quadrilateral circuit with four resistors, \( R_1, R_2, R_3, \) and \( R_4 \), a galvanometer \( G \), and a battery. The galvanometer is connected between the junctions of \( R_2 \) and \( R_3 \), and \( R_1 \) and \( R_4 \). The battery is connected across the bridge. % Correct answer Correct Answer: The condition for no current to flow through the galvanometer is when the bridge is balanced, given by the equation: \[ \frac{R_1}{R_2} = \frac{R_3}{R_4} \]

What is meant by 'relaxation time' of free electrons in a conductor? Show that the resistance of a conductor can be expressed by \( R = \frac{mL}{n e^2 \tau A} \), where symbols have their usual meanings.

Assertion (A): A convex lens, when immersed in a liquid, disappears.
Reason (R): The refractive indices of the material of the lens and the liquid are equal.

Assertion (A): A proton and an electron enter a uniform magnetic field \( \vec{B} \) with the same momentum \( \vec{p} \) such that \( \vec{p} \) is perpendicular to \( \vec{B} \). They describe circular paths of the same radius.
Reason (R): In a magnetic field, orbital radius \( r \) is equal to \( \frac{p}{qB} \).

Assertion (A): Photoelectric effect demonstrates the particle nature of light.
Reason (R): Photoelectric current is proportional to frequency of incident radiation.

Silicon is doped with a pentavalent element. The energy required to set the additional electron free is about:

An electron makes a transition from the \( n = 2 \) level to the \( n = 1 \) level in the Bohr model of a hydrogen atom. Its period of revolution:

Which one of the following is the correct graph between the maximum kinetic energy (\( K_m \)) of the emitted photoelectrons and the frequency of incident radiation (\( \nu \)) for a given photosensitive surface?
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A proton and an alpha particle having equal velocities approach a target nucleus. They come momentarily to rest and then reverse their directions. The ratio of the distance of closest approach of the proton to that of the alpha particle will be:

Which one of the following has the highest frequency?

Consider a solenoid of length \( l \) and area of cross-section \( A \) with a fixed number of turns. The self-inductance of the solenoid will increase if:

The current in a coil of \(15 \, mH}\) increases uniformly from zero to \(4 \, A}\) in \(0.004 \, s}\). Calculate the electromotive force (emf) induced in the coil:

A current carrying circular loop of magnetic moment \( \vec{M} \) is suspended in a vertical plane in an external magnetic field \( \vec{B} \) such that its plane is normal to \( \vec{B} \). The work done in rotating this loop by 45° about an axis perpendicular to \( \vec{B} \) is closest to:

A circular loop of wire, carrying a current 'I' is lying in the xy-plane with its centre coinciding with the origin. It is subjected to a uniform magnetic field pointing along the +z-axis. The loop will:

A 2.0 cm segment of wire, carrying 5.0 A current in positive y-direction lies along the y-axis, as shown in the figure. The magnetic field at a point (3 m, 4 m, 0) due to this segment (part of a circuit) is:

Consider a group of charges \( q_1, q_2, q_3, \ldots \) such that \( \sum q \neq 0 \). Then equipotentials at a large distance, due to this group are approximately:

A telescope consists of two lenses of focal length 100 cm and 5 cm. Find the magnifying power when the final image is formed at infinity.

Draw a labelled ray diagram of a compound microscope showing image formation at least distance of distinct vision. Derive an expression for its magnifying power.

In Young's double-slit experiment using monochromatic light of wavelength \( \lambda \), the intensity of light at a point on the screen, where path difference is \( \lambda \), is \( K \) units. Find the intensity of light at a point on the screen where the path difference is \( \lambda / 6 \).

Give any two differences between the interference pattern obtained in Young's double-slit experiment and a diffraction pattern due to a single slit.

What is current sensitivity of a galvanometer? Show how the current sensitivity of a galvanometer may be increased. Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage sensitivity. Explain.

In a hydrogen atom, the electron moves in an orbit of radius \( 2 \, \text{Å} \) making \( 8 \times 10^{14} \) revolutions per second. Find the magnetic moment associated with the orbital motion of the electron.

A particle of mass \( m \) and charge \( q \) is moving with a velocity \( \vec{v} \) in a magnetic field \( \vec{B} \) as shown in the figure. Show that it follows a helical path. Hence, obtain its frequency of revolution.

State Gauss's law in electrostatics. Apply this to obtain the electric field E at a point near a uniformly charged infinite plane sheet:

Three point charges \( q \), \( 2q \) and \( nq \) are placed at the vertices of an equilateral triangle. If the potential energy of the system is zero, find the value of \( n \).