List of top Questions asked in CBSE CLASS XII

A current of 5 A is passing along +X direction through a wire lying along X-axis. Find the magnetic field \( \vec{B} \) at a point \( \vec{r} = (3 \hat{i} + 4 \hat{j}) \, \text{m} \) due to 1 cm element of the wire, centered at the origin.
A right-angled prism ABC (refractive index \( \sqrt{2} \)) is kept on a plane mirror as shown in the figure. A ray of light is incident normally on the face AC. Trace the path of the ray as it passes through the prism.
Find the angle of deviation produced by the prism.
The magnetic moment (5 J/T) of a bar magnet points along a uniform magnetic field 0.4 T.
“You cannot see a person standing on the other side of a boundary wall but can hear him.” Explain with reason.
A capacitor is charged by a battery to a potential difference \( V \). It is disconnected from the battery and connected across another identical uncharged capacitor. Calculate the ratio of total energy stored in the combination to the initial energy stored in the capacitor.
A capacitor of capacitance \( C \) has reactance \( X \) in an AC circuit. If the capacitance and the frequency of the applied voltage are doubled, the new reactance will become:
“There is a limit to the amount of charge that can be stored on a given capacitor.” Explain.
Find the effective resistance of the network of resistors between points A and F as shown in the figure.
The ends of six wires, each of resistance R
A beam of light of wavelength 720 nm in air enters water (refractive index \( n = \frac{4}{3} \)). Its wavelength in water will be:
Why is the mass of a nucleus always less than the sum of the masses of its constituents, i.e. free neutrons and free protons?
Why is Ampere’s law used for the derivation in magnetic field due to a long straight current-carrying wire of infinite length and not Biot-Savart’s law? Explain.
Use Ampere’s law to derive the expression for the magnetic field due to a long straight current-carrying wire of infinite length.
How is Coulomb repulsion between protons in a nucleus overcome? Explain.
A circular coil of wire having 200 turns, each radius 4.0 cm is placed in a horizontal plane. It carries a current of 0.40 A in the clockwise direction. Find the magnitude and direction of the magnetic field at the center of the coil.
A wire of resistance \( X \, \Omega \) is gradually stretched till its length becomes twice its original length. If its new resistance becomes 40 \( \Omega \), find the value of \( X \).
A glass slab (\( \mu = 1.5 \)) of thickness 6 cm is placed over a paper. The shift in the letters printed on the paper will be:
Write any two advantages of a compound microscope over a simple microscope. Draw a ray diagram for the image formation at the near point by a compound microscope and explain it.
In a refracting telescope, the focal length of the objective is 50 times the focal length of the eyepiece. When the final image is formed at infinity, the length of the tube is 102 cm. Find the focal lengths of the two lenses.
Draw a ray diagram of a reflecting telescope (Cassegrain) and explain the formation of the image. State two important advantages that a reflecting telescope has over a refracting telescope.
The effective capacitance of the network between points A and B shown in the figure is:
effective capacitance of the network between
A transformer is a device used for converting:
The ends of six wires, each of resistance R (= 10 \(\Omega\)) are joined as shown in the figure. The points A and B of the arrangement are connected in a circuit. Find the value of the effective resistance offered by it to the circuit.
The ends of six wires, each of resistance
The currents passing through two inductors of self-inductances 10 mH and 20 mH increase with time at the same rate. Draw graphs showing the variation of:
(I) The magnitude of emf induced with the rate of change of current in each inductor:
(II) The energy stored in each inductor with the current flowing through it:
An electron of mass \(m\) and charge \(-e\) is revolving anticlockwise around the nucleus of an atom. (a) Obtain the expression for the magnetic dipole moment \(\mu\) of the atom.

(b) If \( \vec{L} \) is the angular momentum of the electron, show that:
\[ \vec{\mu} = -\frac{e}{2m} \vec{L} \]