List of top Physics Questions asked in CBSE CLASS XII

In the given figure, three identical bulbs P, Q, and S are connected to a battery.

[(i)] Compare the brightness of bulbs P and Q with that of bulb S when key K is closed.

[(ii)] Compare the brightness of the bulbs S and Q when the key K is opened.
Justify your answer in both cases.

State Lenz’s law. A rod MN of length $ L $ is rotated about an axis passing through its end M perpendicular to its length, with a constant angular velocity $ \omega $ in a uniform magnetic field $ \vec{B} $ parallel to the axis. Obtain an expression for emf induced between its ends.

A voltmeter of resistance 1000 $ \Omega $ can measure up to 25 V. How will you convert it so that it can read up to 250 V?

“There is a limit to the amount of charge that can be stored on a given capacitor.” Explain.

Two coils ‘1’ and ‘2’ are placed close to each other as shown in the figure. Find the direction of induced current in coil ‘1’ in each of the following situations, justifying your answers:

(a) Coil ‘2’ is moving towards coil ‘1’.
(b) Coil ‘2’ is moving away from coil ‘1’.
(c) The resistance connected with coil ‘2’ is increased keeping both the coils stationary.

The given diagram exhibits the relationship between the wavelength of the electromagnetic waves and the energy of photons associated with them. The three points P, Q, and R marked on the diagram may correspond respectively to:

Figure shows variation of Coulomb force (F) acting between two point charges with $ \frac{1}{r^2} $, $ r $ being the separation between the two charges $ (q_1, q_2) $ and $ (q_2, q_3) $. If $ q_2 $ is positive and least in magnitude, then the magnitudes of $ q_1, q_2 $, and $ q_3 $ are such that:

A 1 cm segment of a wire lying along the x-axis carries a current of 0.5 A along the $ +x $-direction. A magnetic field $ \mathbf{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:

Show that the energy required to build up the current $ I $ in a coil of inductance $ L $ is $ \frac{1}{2} L I^2 $.

A current carrying circular loop of area $ A $ produces a magnetic field $ B $ at its centre. Show that the magnetic moment of the loop is: \[ \mu = \frac{2BA}{\mu_0} \sqrt{\frac{A}{\pi}} \]

In the circuit shown, the charge on the left plate of the 20 µF capacitor is $ -50\,\mu C $. The charge on the right plate of the 12 µF capacitor is:

You are required to design an air-filled solenoid of inductance 0.016 H having a length 0.81 m and radius 0.02 m. The number of turns in the solenoid should be:

A current-carrying coil is placed in an external uniform magnetic field. The coil is free to turn in the magnetic field. What is the net force acting on the coil? Obtain the orientation of the coil in stable equilibrium. Show that in this orientation the flux of the total field (field produced by the loop + external field) through the coil is maximum.

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 $.

Explain the following observations using Einstein’s photoelectric equation:
(a) Photoelectric emission does not occur from a surface when the frequency of the light incident on it is less than a certain minimum value.
(b) It is the frequency, and not the intensity of the incident light which affects the maximum kinetic energy of the photoelectrons.
(c) The cut-off voltage $ V_0 $ versus frequency $ \nu $ of the incident light curve is a straight line with a slope $ \frac{h}{e} $.

Using the mirror equation and the formula of magnification, deduce that “the virtual image produced by a convex mirror is always diminished in size and is located between the pole and the focus.”

A battery of emf $ E $ and internal resistance $ r $ is connected to a rheostat. When a current of 2A is drawn from the battery, the potential difference across the rheostat is 5V. The potential difference becomes 4V when a current of 4A is drawn from the battery. Calculate the value of $ E $ and $ r $.

Calculate the mass of an $\alpha$-particle in atomic mass unit (u).
Given: Mass of a normal helium atom = $ 4.002603 \ \text{u} $
Mass of carbon atom = $ 1.9926 \times 10^{-26} \ \text{kg} $

A parallel plate capacitor with plate area $ A $ and plate separation $ d $ has a capacitance $ C_0 $. A slab of dielectric constant $ K $ having area $ A $ and thickness $ \left(\frac{d}{4}\right) $ is inserted in the capacitor, parallel to the plates. Find the new value of its capacitance.

Define electric flux through a surface. Give the significance of a Gaussian surface. A charge outside a Gaussian surface does not contribute to total electric flux through the surface. Why?

A rectangular coil of area A is kept in a uniform magnetic field $\vec{B}$ such that the plane of the coil makes an angle $\alpha$ with $\vec{B}$. The magnetic flux linked with the coil is:

A square loop MNPK of side $ l $ carrying a current $ I_2 $ is kept close to a long straight wire in the same plane and the wire carries a steady current $ I_1 $ as shown in the figure. Obtain the magnitude of magnetic force exerted by the wire on the loop.

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:

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.

In the circuit, three ideal cells of e.m.f. $ V $, $ V $, and $ 2V $ are connected to a resistor of resistance $ R $, a capacitor of capacitance $ C $, and another resistor of resistance $ 2R $ as shown in the figure. In the steady state, find (i) the potential difference between P and Q, (ii) the potential difference across capacitor C.