List of top Physics Questions

A conductor of length \( l \) is connected across an ideal cell of emf \( E \). Keeping the cell connected, the length of the conductor is increased to \( 2l \) by gradually stretching it. If \( R \) and \( R' \) are the initial and final values of resistance, and \( v_d \) and \( v'_d \) are the initial and final values of drift velocity, find the relation between (i) \( R' \) and \( R \) and (ii) \( v'_d \) and \( v_d \).
Two batteries of emfs 3V and 6V and internal resistances 0.2 and 0.4 are connected in parallel. This combination is connected to a 4 resistor. Find:
(i) the equivalent emf of the combination
(ii) the equivalent internal resistance of the combination
(iii) the current drawn from the combination
A p-type Si semiconductor is made by doping an average of one dopant atom per \( 5 \times 10^7 \) silicon atoms. If the number density of silicon atoms in the specimen is \( 5 \times 10^{28} \, \text{atoms/m}^3 \), find the number of holes created per cubic centimetre in the specimen due to doping. Also, give one example of such dopants.
The energy of an electron in an orbit of Bohr hydrogen atom is \( -3.4 \, \text{eV} \). Find its angular momentum.
A spherical convex surface of radius of curvature \( R \) separates glass (refractive index \( 1.5 \)) from air. Light from a point source placed in air at a distance \( \frac{R}{2} \) from the surface falls on it. Find the position and nature of the image formed.
In a Young's double-slit experiment, two light waves, each of intensity \( I_0 \), interfere at a point, having a path difference \( \frac{\lambda}{2} \) on the screen. Find the intensity at this point.
In a diffraction experiment, the slit is illuminated by light of wavelength 600 nm. The first minimum of the pattern falls at \( \theta = 30^\circ \). Calculate the width of the slit.
Show that \( \mathbf{E} = \rho \mathbf{J} \) leads to Ohm's law. Write a condition in which Ohm's law is not valid for a material.

Assertion (A): It is difficult to move a magnet into a coil of large number of turns when the circuit of the coil is closed.
Reason (R): The direction of induced current in a coil with its circuit closed, due to motion of a magnet, is such that it opposes the cause.

Assertion (A): The deflection in a galvanometer is directly proportional to the current passing through it.
Reason (R): The coil of a galvanometer is suspended in a uniform radial magnetic field.

Assertion (A): We cannot form a p-n junction diode by taking a slab of a p-type semiconductor and physically joining it to another slab of an n-type semiconductor.
Reason (R): In a p-type semiconductor, \( n_e \gg n_h \) while in an n-type semiconductor \( n_h \gg n_e \).

Assertion (A): The potential energy of an electron revolving in any stationary orbit in a hydrogen atom is positive. 
Reason (R): The total energy of a charged particle is always positive.

Let \( \lambda_e \), \( \lambda_p \), and \( \lambda_d \) be the wavelengths associated with an electron, a proton, and a deuteron, all moving with the same speed. Then the correct relation between them is:
When a p-n junction diode is forward biased:
Which of the following figures correctly represent the shape of the curve of binding energy per nucleon as a function of mass number?
A source produces monochromatic light of frequency \( 5.0 \times 10^{14} \, \text{Hz} \) and the power emitted is 3.31 mW. The number of photons emitted per second by the source, on an average, is:
The speed of light in two media '1' and '2' are \( v_1 \) and \( v_2 \) (\( v_2>v_1 \)) respectively. For a ray of light to undergo total internal reflection at the interface of these two media, it must be incident from:
Which one of the following correctly represents the change in wave characteristics (all in vacuum) from microwaves to X-rays in electromagnetic spectrum?
A voltage \( v = v_0 \sin(\omega t) \) applied to a circuit drives a current \( i = i_0 \sin(\omega t + \phi) \) in the circuit. The average power consumed in the circuit over a cycle is:
You are required to design an air-filled solenoid of inductance \( 0.016 \, \text{H} \) having a length \( 0.81 \, \text{m} \) and radius \( 0.02 \, \text{m} \). The number of turns in the solenoid should be:

A circular coil of diameter 15 mm having 300 turns is placed in a magnetic field of 30 mT such that the plane of the coil is perpendicular to the direction of the magnetic field. The magnetic field is reduced uniformly to zero in 20 ms and again increased uniformly to 30 mT in 40 ms. If the EMFs induced in the two time intervals are \( e_1 \) and \( e_2 \) respectively, then the value of \( e_1 / e_2 \) is:

A 1 cm segment of a wire lying along the x-axis carries current of \( 0.5 \, A \) along the \( +x \)-direction. A magnetic field \( \vec{B} = (0.4 \, \text{mT}) \hat{j} + (0.6 \, \text{mT}) \hat{k} \) is switched on, in the region. The force acting on the segment is:
The resistance of a wire of length \( L \) and radius \( r \) is \( R \). Which one of the following would provide a wire of the same material with resistance \( \frac{R}{2} \)?
A beam of light coming from a distant source is refracted by a spherical glass ball (refractive index 1.5) of radius 15 cm. Draw the ray diagram and obtain the position of the final image formed.
Define a wavefront. An incident plane wave falls on a convex lens and gets refracted through it. Draw a diagram to show the incident and re fracted wavefront.