Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions

The total current in a semiconductor is ______.

The electric potential inside a conducting sphere ______.

Which of the following about potential at a point due to a given point charge is true?

The potential at a point P due to a given point charge ______.

A generator has an e.m.f. of 440 Volt and internal resistance of 4000 hm. Its terminals are connected to a load of 4000 ohm. The voltage across the load is ______.

There is a uniform magnetic field directed perpendicular and into the plane of the paper. An irregular shaped conducting loop is slowly changing into a circular loop in the plane of the paper. Then ______.

A metal plate can be heated by ______.

How long can an electric lamp of 100 W be kept glowing by fusion of 2 kg of deuterium? Take the fusion reaction as 

\[\ce{​​^2_1H + ^2_1H -> ^3_2He + n + 3.27 MeV}​​\]

The focal length of a convex lens made of glass of refractive index (1.5) is 20 cm.

What will be its new focal length when placed in a medium of refractive index 1.25?

Is focal length positive or negative? What does it signify?

Calculate potential on the axis of a ring due to charge Q uniformly distributed along the ring of radius R.

Calculate potential on the axis of a disc of radius R due to a charge Q uniformly distributed on its surface.

The primary origin(s) of magnetism lies in ______.

1. atomic currents.
2. pauli exclusion principle.
3. polar nature of molecules.
4. intrinsic spin of electron.

Three identical bar magnets are rivetted together at centre in the same plane as shown in figure. This system is placed at rest in a slowly varying magnetic field. It is found that the system of magnets does not show any motion. The north-south poles of one magnet is shown in the figure. Determine the poles of the remaining two.

You are given four sources of light each one providing a light of a single colour – red, blue, green and yellow. Suppose the angle of refraction for a beam of yellow light corresponding to a particular angle of incidence at the interface of two media is 90°. Which of the following statements is correct if the source of yellow light is replaced with that of other lights without changing the angle of incidence?

The radius of curvature of the curved surface of a plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will ______.

The direction of ray of light incident on a concave mirror is shown by PQ while directions in which the ray would travel after reflection is shown by four rays marked 1, 2, 3 and 4 (figure). Which of the four rays correctly shows the direction of reflected ray?