Science (English Medium) कक्षा १२ - CBSE Important Questions for Physics

Define the term polarization of a dielectric and write the expression for a linear isotropic dielectric in  terms of electric field.

Answer the following question.
Describe briefly the process of transferring the charge between the two plates of a parallel plate capacitor when connected to a battery. Derive an expression for the energy stored in a capacitor.

Solve the following question.
A parallel plate capacitor is charged by a battery to a potential difference V. It is disconnected from the battery and then connected to another uncharged capacitor of the same capacitance. Calculate the ratio of the energy stored in the combination to the initial energy on the single capacitor.   

Two identical point charges, q each, are kept 2m apart in the air. A third point charge Q of unknown magnitude and sign is placed on the line joining the charges such that the system remains in equilibrium. Find the position and nature of Q.

A point charge is placed at the centre of a hollow conducting sphere of internal radius ‘r’ and outer radius ‘2r’. The ratio of the surface charge density of the inner surface to that of the outer surface will be ______.

The physical quantity having SI unit NC^–1m is ______.

Obtain the expression for the energy stored in a capacitor connected across a dc battery. Hence define energy density of the capacitor

Two-point charges q₁ and q₂ are kept at a distance of r₁₂ in air. Deduce the expression for the electrostatic potential energy of this system.

If an external electric field (E) is applied on the system, write the expression for the total energy of this system.

The magnitude of the electric field (in NC ^{– 1}) in a region varies with the distance r(in m) as

E = 10 r + 5

By how much does the electric potential increase in moving from point at r = 1 m to a point at r = 10 m.

The variation of inductive reactance (X_L) of an inductor with the frequency (f) of the ac source of 100 V and variable frequency is shown in fig.

1. Calculate the self-inductance of the inductor.
2. When this inductor is used in series with a capacitor of unknown value and a resistor of 10 Ω at 300 s^–1, maximum power dissipation occurs in the circuit. Calculate the capacitance of the capacitor.

Two cells of emfs 1.5 V and 2.0 V,  having internal resistances 0.2 Ω and 0.3 Ω, respectively, are connected in parallel. Calculate the emf and internal resistance of the equivalent cell.

Define the term drift velocity.

In the following potentiometer circuit, AB is a uniform wire of length 1 m and resistance 10 Ω. Calculate the potential gradient along the wire and balance length AO (= l).

Write its (‘mobility’ of charge carriers) S.I. unit

A low voltage supply from which one needs high currents must have very low internal resistance. Why?

Nichrome and copper wires of same length and same radius are connected in series. Current I is passed through them. Which wire gets heated up more? Justify your answer.

Write the principle of working of a metre bridge

In a metre bridge, the balance point is found at a distance l₁ with resistances R and S as shown in the figure.An unknown resistance X is now connected in parallel to the resistance S and the balance point is found at a distance l₂. Obtain a formula for X in terms of l₁, l₂ and S. 

On the basis of electron drift, derive an expression for resistivity of a conductor in terms of number density of free electrons and relaxation time. On what factors does resistivity of a conductor depend?