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 VA–VB positive, negative or zero? [CBSE Delhi 2016]
Ans. The potential due to a point charge decreases with increase of distance. So, VA – VB is positive. Explanation: Let the distance of point A and B from charge Q be rA and rB respectively.
Q. 5. A point charge Q is placed at point ‘O’ as shown in figure. Is the potential at point A, i.e., VA, greater, smaller or equal to potential, VB, 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., VA = VB.
∴ Work done in moving charge q0=10 μC from A to B is
W = q0 (VB – VA) = 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 VA – VB 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.
VA – VB > 0 ⇒ VA > VB
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 VAB = 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 (VB – VA) = q (VA – VA) = 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.