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

Define electric dipole moment. Is it a scalar or a vector? Derive the expression for the electric field of a dipole at a point on the equatorial plane of the dipole.

Using Gauss’ law deduce the expression for the electric field due to a uniformly charged spherical conducting shell of radius R at a point

(i) outside and (ii) inside the shell.

Plot a graph showing variation of electric field as a function of r > R and r < R.

(r being the distance from the centre of the shell)

Using Gauss’s law, prove that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance from it.

How is the field directed if (i) the sheet is positively charged, (ii) negatively charged?

An infinitely long positively charged straight wire has a linear charge density λ. An electron is revolving in a circle with a constant speed v such that the wire passes through the centre, and is perpendicular to the plane, of the circle. Find the kinetic energy of the electron in terms of the magnitudes of its charge and linear charge density λ on the wire.

Draw a graph of kinetic energy as a function of linear charge density λ.

Consider two identical point charges located at points (0, 0) and (a, 0).

Is there a point on the line joining them at which the electric field is zero?

Consider two identical point charges located at points (0, 0) and (a, 0).

Is there a point on the line joining them at which the electric potential is zero?

Define mobility of a charge carrier

Define capacitor reactance. Write its S.I units.

Two capacitors of unknown capacitances C₁ and C₂ are connected first in series and then in parallel across a battery of 100 V. If the energy stored in the two combinations is 0.045 J and 0.25 J respectively, determine the value of C₁ and C₂. Also calculate the charge on each capacitor in parallel combination.

Define the terms polarization of a dielectric and write its relation with susceptibility.

A capacitor 'C', a variable resistor 'R' and a bulb 'B' are connected in series to the ac mains in circuit as shown. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between the plates of the capacitor, keeping resistance R to be the same; (ii) the resistance R is increased keeping the same capacitance?

Obtain the expression for the energy stored per unit volume in a charged parallel plate capacitor.

The electric field inside a parallel plate capacitor is E. Find the amount of work done in moving a charge q over a closed loop a b c d a.

Derive the expression for the capacitance of a parallel plate capacitor having plate area A and plate separation d.

Two charged spherical conductors of radii R₁ and R₂ when connected by a conducting wire acquire charges q₁ and q₂ respectively. Find the ratio of their surface charge densities in terms of their radii.

Considering the case of a parallel plate capacitor being charged, show how one is required to generalize Ampere's circuital law to include the term due to displacement current.

A parallel plate capacitor of capacitance C is charged to a potential V. It is then connected to another uncharged capacitor having the same capacitance. Find out the ratio of the energy stored in the combined system to that stored initially in the single capacitor.

Find out the amount of the work done to separate the charges at infinite distance.