# Chapter 2 Electrostatic Potential and Capacitance – Important 1 Mark Questions Class 12 CBSE Physics PYQ

**Previous Year Questions-Important 1 Mark Questions Chapter 2 Electrostatic Potential and Capacitance Class 12 CBSE Physics**

**Q. 1.** **Name the physical quantity whose SI unit is J/C. Is it a scalar or a vector quantity? [CBSE Delhi 2010]**

**Ans**. Electric potential. It is a scalar quantity.

**Q. 2. Figure shows the field lines on a positive charge. Is the work done by the field in moving a small positive charge from Q to P positive or negative? Give reason. [CBSE (F) 2014]**

**Ans.** The work done by the field is negative. This is because the charge is moved against the force exerted by the field.

**Q. 3. The field lines of a negative point charge are as shown in the figure. Does the kinetic energy of a small negative charge increase or decrease in going from B to A? [CBSE Patna 2015]**

**Ans.** The kinetic energy of a negative charge decreases while going from point B to point A, against the movement of force of repulsion.

**Q. 4. A point charge +Q is placed at point O as shown in the figure. Is the potential difference V _{A}–V_{B} positive, negative or zero? [CBSE Delhi 2016]**

**Ans**. The potential due to a point charge decreases with increase of distance. So, V_{A} – V_{B} is positive. **Explanation:** Let the distance of point A and B from charge Q be r_{A }and r_{B }respectively.

**Q. 5. A point charge Q is placed at point ‘O’ as shown in figure. Is the potential at point A, i.e., V _{A}, greater, smaller or equal to potential, V_{B}, at point B, when Q is (i) positive, and (ii) negative charge? [CBSE (F) 2017]**

**Ans. **

**Q. 7. A 500 μC charge is at the centre of a square of side 10 cm. Find the work done in moving a charge of 10 μC between two diagonally opposite points on the square. [CBSE Delhi 2008]**

**Ans.**

The points A and B are equidistant from the centre of square where charge q = 500 μC is located; therefore, points A and B are at the same potential i.e., V_{A} = V_{B}.

∴ Work done in moving charge q_{0}=10 μC from A to B is

W = q_{0} (V_{B} – V_{A}) = 0

**Q. 7. Draw an equipotential surface in a uniform electric field. [CBSE (AI) 2008]**

**Ans.**

**Q. 8. A point charge Q is placed at point O as shown in the figure. The potential difference V _{A} – V_{B} is positive. Is the charge Q negative or positive? [CBSE (F) 2016]**

**Ans.**

The potential due to a point charge decreases with increase of distance.

V_{A} – V_{B} > 0 ⇒ V_{A} > V_{B}

Hence, the charge Q is positive.

**Q. 9. Depict the equipotential surfaces for a system of two identical positive point charges placed a distance ‘d’ apart. [CBSE Delhi 2010]**

Ans. Equipotential surfaces due to two identical charges is shown in figure.

**Q. 10. Draw an equipotential surface for a system consisting of two charges Q, – Q separated by a distance r in air. Locate the points where the potential due to the dipole is zero. [CBSE Delhi 2017, (AI) 2008, 2013]**

**Ans.** The equipotential surface for the system is as shown. Electric potential is zero at all points in the plane passing through the dipole equator AB.

**Q. 11. Why do the equipotential surfaces due to a uniform electric field not intersect each other? [CBSE (F) 2012]**

Ans. This is because, at the point of intersection there will be two values of electric potential, which is not possible.

**Q. 12. “For any charge configuration, equipotential surface through a point is normal to the electric field.” Justify. [CBSE Delhi 2014]**

Ans. The work done in moving a charge from one point to another on an equipotential surface is zero. If electric field is not normal to the equipotential surface, it would have non-zero component along the surface. In that case work would be done in moving a charge on an equipotential surface.

**Q. 13. Why is the potential inside a hollow spherical charged conductor constant and has the same value as on its surface? [CBSE (F) 2012]**

Ans. Electric field intensity is zero inside the hollow spherical charged conductor. So, no work is done in moving a test charge inside the conductor and on its surface. Therefore, there is no potential difference between any two points inside or on the surface of the conductor.

**Q. 14. A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. What is the potential at the centre of the sphere? [CBSE (AI) 2011]**

Ans. Potential at centre of sphere = 10 V. Potential at all points inside the hollow metal sphere (or any surface) is always equal to the potential at its surface.

**Q. 15. A charge ‘q’ is moved from a point A above a dipole of dipole moment ‘p’ to a point B below the dipole in equatorial plane without acceleration. Find the work done in the process. [CBSE Central 2016]**

Ans. Work done in the process is zero. Because, equatorial plane of a dipole is equipotential surface and work done in moving charge on equipotential surface is zero.

W = q V_{AB} = q × 0 = 0

**Q. 16. Why is there no work done in moving a charge from one point to another on an equipotential surface? [CBSE (F) 2012]**

Ans. The potential difference between any two points of equipotential surface is zero. We have

**Q. 17. What is the work done in moving a test charge q through a distance of 1 cm along the equatorial axis of an electric dipole? [CBSE (AI) 2009]**

Ans. At every point on equatorial axis, the potential is zero, so work done

W = q ∆V = 0 (zero).

**Q. 18. Figure shows the field lines due to a negative point charge. Give the sign of the potential energy difference of a small negative charge between the points A and B. [CBSE (F) 2014]**

Ans.

**Q. 19. What is the amount of work done in moving a point charge Q around a circular arc of radius ‘r’ at the centre of which another point charge ‘q’ is located? [CBSE North 2016]**

Ans. The potential of points A and B are same being equal to

Where R is the radius of the circle.

Work done W= q (V_{B} – V_{A}) = q (V_{A} – V_{A}) = 0.

**Q. 20. A metal plate is introduced between the plates of a charged parallel plate capacitor. What is its effect on the capacitance of the capacitor? [CBSE (F) 2009]**

Ans. By introducing the metal plate between the plates of charged capacitor, the capacitance of capacitor increases**Reason:** It t is thickness of metal plate, then

**Q. 21. The figure shows the field lines of a positive point charge. What will be the sign of the potential energy difference of a small negative charge between the points Q and P? Justify your answer. [CBSE Guwahati 2015]**

Ans.

The sign of the potential energy difference of a small negative charge will be positive. This is because negative charge moves a point at a lower potential energy to a point at a higher potential energy.