Science (English Medium) Class 12 - CBSE Important Questions

Depict the equipotential surfaces for a system of two identical positive point charges placed a distance(d) apart?

Deduce the expression for the potential energy of a system of two point charges q₁ and q₂ brought from infinity to the points `vecr_1`and `vecr_2`respectively in the presence of external electric field `vecE`.

A parallel-plate capacitor is charged to a potential difference V by a dc source. The capacitor is then disconnected from the source. If the distance between the plates is doubled, state with reason how the following change:

(i) electric field between the plates

(ii) capacitance, and

(iii) energy stored in the capacitor

Can two equi-potential surfaces intersect each other? Give reasons.

Two charges −q and +q are located at points A (0, 0, −a) and B (0, 0, +a) respectively. How much work is done in moving a test charge from point P (7, 0, 0) to Q (−3, 0, 0)?

Three identical capacitors C₁, C₂ and C₃ of capacitance 6 μF each are connected to a 12 V battery as shown.

Find

(i) charge on each capacitor

(ii) equivalent capacitance of the network

(iii) energy stored in the network of capacitors

The figure show a network of five capacitors connected to a 10V battery. Calculate the charge acquired by the 5μF capacitor.

An ac circuit consists of a series combination of circuit elements X and Y. The current is ahead of the voltage  in phase by `pi /4` . If element X is a pure resistor of 100Ω ,

(a)  name the circuit element Y.
(b)  calculate the rms value of current, if rms value of voltage is  141V.
(c)  what will happen if the ac source is replaced by a dc source ?

Derive an expression for the electric potential at any point along the axial line of an electric dipole.

Draw the equipotential surfaces due to an electric dipole.

The figure shows a network of five capacitors connected to a 100 V supply. Calculate the total energy stored in the network.

An ac circuit consists of a series combination of circuit elements X and Y. The current is ahead of the voltage in phase by `pi/4`. If element X is a pure resistor of 100 Ω,

(a) name the circuit element Y.

(b) calculate the rms value of current, if rms of voltage is 141 V.

(c) what will happen if the ac source is replaced by a dc source

Define the dielectric constant of a medium. What is its S.I unit?

Three circuits, each consisting of a switch 'S' and two capacitors, are initially charged, as shown in the figure. After the switch has been closed, in which circuit will the charge on the left-hand capacitor
(i) increase,
(ii) decrease, and
(iii) remains the same? Give reasons.

Two parallel uniformly charged infinite plane sheets, '1' and '2', have charge densities + `sigma and -2sigma `respectively. Give the magnitude and direction of the net electric field at a point.
(i) in between the two sheets and
(ii) outside near the sheet '1'.

Define electrostatic potential at a point. Write its S.I. unit. Three-point charges q1, q2 and q3 are kept respectively at points A, B, and C as shown in the figure, Derive the expression for the electrostatic potential energy of the system.

Depict the equipotential surface due to
(i) an electric dipole,
(ii) two identical positive charges separated by a distance.

Obtain the expression for capacitance for a parallel plate capacitor.

Which of the following is NOT the property of equipotential surface?

• Assertion (A): An electron has a high potential energy when it is at a location associated with a more negative value of potential, and a low potential energy when at a location associated with a more positive potential.
• Reason (R): Electrons move from a region of higher potential to region of lower potential.

Select the most appropriate answer from the options given below: