List of top Questions asked in CBSE CLASS XII

The process of mineralization by microorganisms helps in the release of:
Transplantation of tissues/organs to some patients often fails due to rejection by the body of the patient. Which type of immune response is responsible for such rejections?
A man whose father was colour-blind marries a woman who had a colour-blind mother and normal father. What percentage of male children of this couple will be colour-blind?
If the projection of \( \mathbf{a} = \alpha \hat{i} + \hat{j} + 4 \hat{k} \) on \( \mathbf{b} = 2 \hat{i} + 6 \hat{j} + 3 \hat{k} \) is 4 units, then \( \alpha \) is:
A 1 cm straight segment of a conductor carrying 1 A current in \( x \)-direction lies symmetrically at the origin of Cartesian coordinate system. The magnetic field due to this segment at point (1m, 1m, 0) is:
Two long solenoids of radii \( r_1 \) and \( r_2 \) (\( > r_1 \)) and number of turns per unit length \( n_1 \) and \( n_2 \) respectively are co-axially wrapped one over the other. The ratio of self-inductance of inner solenoid to their mutual inductance is:
The focal length of a concave mirror in air is \( f \). When the mirror is immersed in a liquid of refractive index \( \frac{3}{5} \), its focal length will become:
A diamagnetic substance is brought, one by one, near the north pole and the south pole of a bar magnet. It is:
Atomic spectral emission lines of hydrogen atom are incident on a zinc surface. The lines which can emit photoelectrons from the surface are members of:
A coil of an AC generator, having 100 turns and area 0.1 m² each, rotates at half a rotation per second in a magnetic field of 0.02 T. The maximum emf generated in the coil is:
Which one of the following statements is correct? Electric field due to static charges is:
When the resistance measured between p and n ends of a p-n junction diode is high, it can act as a/an:
The energy of an electron in a hydrogen atom in ground state is -13.6 eV. Its energy in an orbit corresponding to quantum number \( n \) is -0.544 eV. The value of \( n \) is:

Assertion : Out of Infrared and radio waves, the radio waves show more diffraction effect.

Reason (R): Radio waves have greater frequency than infrared waves.

Assertion : In an ideal step-down transformer, the electrical energy is not lost.

Reason (R): In a step-down transformer, voltage decreases but the current increases.

Assertion : In Bohr model of hydrogen atom, the angular momentum of an electron in \( n \)th orbit is proportional to the square root of its orbit radius \( r_n \)

Reason (R): According to Bohr model, electron can jump to its nearest orbits only.

Assertion : In a semiconductor diode, the thickness of the depletion layer is not fixed.

Reason (R): Thickness of depletion layer in a semiconductor device depends upon many factors such as biasing of the semiconductor.

Define resistivity of a conductor. Discuss its dependence on temperature of the conductor and draw a plot of resistivity of copper as a function of temperature.
"A low voltage battery from which high current is required must have low internal resistance." Justify.
"A high voltage battery must have a large internal resistance." Justify.
When a parallel beam of light enters water surface obliquely at some angle, what is the effect on the width of the beam?
With the help of a ray diagram, show that a straw appears bent when it is partly dipped in water and explain it.
How is an electromagnetic wave produced?
An electromagnetic wave is travelling in vertically upward direction. At an instant, its electric field vector points in west direction. In which direction does the magnetic field vector point at that instant?
Estimate the ratio of shortest wavelength of radio waves to the longest wavelength of gamma waves.