List of top Questions asked in CBSE CLASS XII

The magnetic flux linked with a closed coil (in Wb) varies with time \( t \) (in s) as \( \phi = 5t^2 + 4t - 2 \). If the resistance of the circuit is 14 \( \Omega \), the magnitude of induced current in the coil at \( t = 1 \) s will be:
In an electromagnetic wave travelling in free space, the amplitude of magnetic field is \( 6.0 \times 10^{-4} \ \text{T} \). The amplitude of its electric field is:
The two surfaces of a biconvex lens are of radius of curvature \( R \) each. Obtain the condition under which its focal length \( f \) is equal to \( R \). If one of the two surfaces of this lens is made plane, what will be the new focal length of the lens?
In which cases does a charged particle not experience a force in a magnetic field?
A bar magnet is held with its length along the axis of a closed coil. Initially, the south pole of the magnet faces the coil. If the magnet is moved towards the coil, explain how a current is induced in the coil and in what direction.
Define ‘wavefront’ of a light wave. A plane wavefront is refracted from a convex lens. Draw the shape of the refracted wavefront.
A plane wave travelling in a medium is incident on a plane surface separating this medium from a rarer medium. Draw a diagram to show refraction of the wave. Hence, verify Snell’s law.
The above battery sends a current \( I_1 \) when \( R = R_1 \) and a current \( I_2 \) when \( R = R_2 \). Obtain the internal resistance of the battery in terms of \( I_1 \), \( I_2 \), \( R_1 \), and \( R_2 \).
Two point charges Q and \( -q \) are held \( r \) distance apart in free space. A uniform electric field \( \vec{E} \) is applied in the region perpendicular to the line joining the two charges. Which one of the following angles will the direction of the net force acting on charge \( -q \) make with the line joining Q and \( -q \)?
Three wires A, B, and C of the same material have lengths and area of cross-sections as \( (2l, \frac{A}{2}) \), \( (l, A) \) and \( (\frac{l}{2}, 2A) \), respectively. If the resistances of these wires are \( R_A, R_B, R_C \) respectively, then:
A particle of mass \( m \) and charge \( q \) moves along the y-axis in a region in which a uniform magnetic field \( \vec{B} \) is pointing along the x-axis. The Lorentz force acting on the charge will point along:
The electric field in space between the plates of a parallel plate capacitor (each of area \( 2.5 \times 10^{-3} \, \text{m}^2 \)) is changing at the rate of \( 4 \times 10^6 \, \text{Vm}^{-1}\text{s}^{-1} \). The displacement current between the plates of the capacitor is :
In a double slit experiment, the two slits are 1.5 mm apart. The slits are illuminated by a mixture of lights of wavelengths of 600 nm and 400 nm, and the interference pattern is observed on a screen 1.5 m away from the slits. Find the minimum distance of the point from the central maximum at which bright fringes of the interference patterns of the two wavelengths coincide.
Find the focal length of the plano-convex lens of refractive index 1.5 and radius of curvature 10 cm when it is immersed in a liquid of refractive index 1.25.
Find the ratio of minimum to maximum wavelength of radiations emitted when an electron jumps from higher energy state into ground state of hydrogen atom.
A charged particle \(q\) moving with a velocity \( \mathbf{v} \) is subjected to a uniform magnetic field \( \mathbf{B} \) acting perpendicular to \( \mathbf{v} \). If a uniform electric field \( \mathbf{E} \) is also set up in the region along the direction of \( \mathbf{B} \), describe the path followed by the particle and draw its shape.
How will the magnetic field inside a long solenoid be affected when:
(i) the radius of the turns of the solenoid is increased,
(ii) the length of the solenoid as well as the total number of its turns are doubled?
A physics teacher wants to demonstrate interference with the help of double slit experiment using a laser beam of 633 nm wavelength. Since the hall is large enough, interference pattern is formed on the wall 5.0 m from the slits. For clear and comfortable view by all the students they want the fringe width 5 mm.
A parallel beam of light of wavelength 650 nm passes through a slit of width 0.6 mm. The diffraction pattern is obtained on a screen kept 60 cm away from the slit. Find the distance between first order minima on both sides of the central maximum.
When the switch of the circuit is turned on, the filament of the bulb glows instantaneously because:
A particle with charge \( q \) moving with velocity \( \vec{v} = v_0 \hat{i} \) enters a region with magnetic field \( \vec{B} = B_1 \hat{j} + B_2 \hat{k} \). The magnitude of force experienced by the particle is:
The materials having negative magnetic susceptibility are :
When current in a coil changes at a steady rate from 8 A to 6 A in 4 ms, an emf of 1.5 V is induced in it. The value of self-inductance of the coil is :
Show that Gauss’s theorem is consistent with Coulomb’s law. Using it, derive an expression for the electric field due to a uniformly charged thin spherical shell of radius r at a point at a distance y from the centre of the shell such that:
(I) y>r, and
(II) y<r.
A point charge of +2 nC is kept at the origin of a three-dimensional coordinate system. Find the type and magnitude of the charge which should be kept at (0, 0, −6 m) so that the potential due to the system becomes zero at (0, 0, 2 m).