List of top Physics Questions asked in CBSE CLASS XII

Who first produced and observed EM waves in the 25mm-5mm range?

Charges Q1, Q2, and Q3 are at (-d,0), (0,0), and (d,0). Q1=Q3, Q2>0. Find the nature and value of Q1 for zero potential energy.

How does conductivity of an intrinsic semiconductor vary with temperature? Show in a plot.

An object is placed 30 cm in front of a concave mirror (radius of curvature 40 cm). Find: (i) image position (ii) magnification

Two batteries (6V, 0.8Ω and 3V, 0.2Ω) are connected in series with external resistance R. Find R so that the potential difference across the 6V battery is zero.

A bar magnet (2.5 J/T) is aligned with a 0.32 T field. (a) Find work done to align it (i) normal, (ii) opposite to the field. (b) Find torque in both cases.

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 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.

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.

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 ? 
 

An electric dipole consists of point charges $-1.0 \, \mathrm{pC}$ and $+1.0 \, \mathrm{pC}$ located at $(0, 0)$ and $(3 \, \mathrm{mm}, 4 \, \mathrm{mm})$ respectively in the $x$–$y$ plane. An electric field $\vec{E} = \left( 1000 \, \mathrm{V/m} \right) \, \hat{i}$ is switched on in the region. Find the torque $\vec{\tau}$ acting on the dipole.
 

Two isolated metallic spheres $S_1$ and $S_2$ of radii $1 \, \mathrm{cm}$ and $3 \, \mathrm{cm}$ respectively are charged such that both have the same charge density  \[ \sigma = \frac{2}{\pi} \times 10^{-9} \, \mathrm{C/m^2}. \] They are placed far away from each other and connected by a thin wire. Calculate the new charge on sphere $S_1$.
 

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.

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.

What are the coherent sources of light? Can two independent sodium lamps act like coherent sources? Explain.