List of top Physics Questions asked in CBSE CLASS XII

A wire bent into circular loop A carries current I. The same wire is bent into loop B with two turns, same current. Find the ratio of magnetic fields at the centers of A to B.
Electric and magnetic fields of EM waves are:
A conducting circular loop (radius shrinking at 1 mm/s) is in a uniform magnetic field B = 50 mT, plane perpendicular to the field. Find the induced emf when the radius is 4 cm.
Four cells (emf E, internal resistance r) are connected in series, but one is wrongly connected. Find the equivalent emf and internal resistance.
Two beams (3.3 eV and 11.3 eV) illuminate a metal (work function 2.3 eV). Find the ratio of maximum electron speeds.
An electron and a proton have the same wavelength λ. This implies they have the same:
A charged sphere (radius r, surface charge density σ) has electric field E. If the radius doubles (charge density constant), what's the ratio of the old to new electric field?
State any two properties of a nucleus.
The above two parts are kept in contact with each other as shown in the figure. The power of the combination will be: The above two parts are kept in contact
A signal, as shown in the figure, is applied to a p-n junction diode. Identify the output across the resistance \( R_L \):
Derive an expression for potential energy of an electric dipole $\vec{p}$ in an external uniform electric field $\vec{E}$. When is the potential energy of the dipole (1) maximum, and (2) minimum ? 
 
A resistor and a capacitor are connected in series to an AC source $v = v_m \sin \omega t$. Derive an expression for the impedance of the circuit.

An electric lamp is designed to operate at $110 \, \mathrm{V} $ DC and $11 \, \mathrm{A}$ current. If the lamp is operated on $220 \, \mathrm{V}$, $50 \, \mathrm{Hz}$ AC source with a coil in series, then find the inductance of the coil.Correct Answer: 
The inductance of the coil is $L = 0.064 \, \mathrm{H}$.

A ray of light is incident normally on a refracting face of a prism of prism angle $A$ and suffers a deviation of angle $\delta$. Prove that the refractive index $n$ of the material of the prism is given by: \[ n = \frac{\sin(A + \delta)}{\sin A}. \]
The refractive index of the material of a prism is $\sqrt{2}$. If the refracting angle of the prism is $60^\circ$, find:
1. The angle of minimum deviation, and 
2. The angle of incidence.
State Huygens’ principle. A plane wave is incident at an angle $i$ on a reflecting surface. Construct the corresponding reflected wavefront. Using this diagram, prove that the angle of reflection is equal to the angle of incidence.
What are the coherent sources of light? Can two independent sodium lamps act like coherent sources? Explain.
A beam of light consisting of a known wavelength 520nm and an unknown wavelength λ, used in Young’s double slit experiment, produces two interference patterns such that the fourth bright fringe of unknown wavelength coincides with the fifth bright fringe of known wavelength. Find the value of λ
(i) Draw a labelled diagram of a step-up transformer and describe its working principle. Explain any three causes for energy losses in a real transformer.
(ii) A step-up transformer converts a low voltage into high voltage. Does it violate the principle of conservation of energy? Explain.
(iii) A step-up transformer has 200 and 3000 turns in its primary and secondary coils respectively. The input voltage given to the primary coil is 90V. Calculate:
1. The output voltage across the secondary coil.
2. The current in the primary coil if the current in the secondary coil is 2.0A.
A step-up transformer converts a low voltage into high voltage. Does it violate the principle of conservation of energy? Explain.
When does an inductor act as a conductor in a circuit? Give reason for it.
An electric dipole (dipole moment $\vec{p} = p \, \hat{i}$), consisting of charges $-q$ and $q$, separated by distance $2a$, is placed along the $x$-axis, with its center at the origin. Show that the potential $V$, due to this dipole, at a point $x$ ($x \gg a$) is equal to: \[ V = \frac{1}{4\pi\epsilon_0} \cdot \frac{\vec{p} \cdot \hat{i}}{x^2}. \]
In a full-wave rectifier:
An alternating voltage of frequency \( 50 \, \text{Hz} \) is applied to a half-wave rectifier. Then the ripple frequency of the output will be:
In a full-wave rectifier, the current in each of the diodes flows for: