Conceptual Questions Based On Electric Potential

Q.1. Why earth is considered to be at zero potential?
Answer: Earth has very large size. Potential of earth does not change with small charge therefore it is considered as reference level and potential taken as zero.

Q.2. If electric potential V within a certain region is constant, what is the nature of electric field inside the
region?

Answer: Since electric field is negative of the potential gradient therefore if the electric potential is constant
in a certain region then potential gradient or electric field intensity is zero.

Q.3. Can two equipotential surfaces intersect?
Answer: Equipotential surface is the one having same potential everywhere, if two potential surfaces intersect then at the point of intersection there will be two values of the potential.

Q.4. If potential at a point is zero, is field at that point is zero?
Answer: No, if potential at a point is zero, field may not be zero as in the case of equatorial line of dipole
where the potential is zero but the field intensity is not zero.

Q.5. Can we produce high potential on a body without getting the shock?
Answer: Yes, we can do so if we are standing on an insulating stand and we touch a high power line. This can
happen as charge or potential on the body is never dangerous the flow of charge through the body is
dangerous.

Q.6. What is the importance of Gaussian surface?
Answer: Gaussian surface helps us in evaluating the electric field intensity at a given point for the symmetric
charge distribution.

Q.7. Near the surface of earth there is an electric field of the order of 100KV/m. Why then do we not
experience shock?

Answer: Our body and earth are at the same potential therefore although there is large field there is no potential difference between our body and earth and we will not experience shock as no flow of charge is
there.

Q.8. If two electrons are brought near each other, what happens to their potential energy?
Answer: If two similar charges are brought closer the stability of the system decreases because of repulsion
between them thus the potential energy

Q.9. Will there be effect in the potential if the medium around the charge is changed?
Answer: Yes, medium effects the potential around the charge. With increase in dielectric constant of the
medium the potential around the charge goes on decreasing.

Q.10. What is the shape of the equipotential surface for the point charge and for the line charge?
Answer: The equipotential surface is one with same potential everywhere on it. For point charge the locus of
points having same potential will be sphere and for line charge its cylinder. Therefore equipotential
surface for point charge is sphere and for line charge it is cylinder.

Q.11. A charge Q is placed at any point and another charge q is rotated along the semi-circular path along
P. calculate he work done against the electric field of Q?

Answer: As the directions of lines of force is radial to the path followed by the charge on the circular path.
Therefore work done in motion along circular path is always zero..

Q.12. What is the work done by the field of nucleus in complete circular or elliptical orbit?
Answer: For the complete orbit the displacement is zero therefore work done will also be zero

Q.13. Consider a long conductor, the middle of which is earthed. If the potential difference across the two
ends of the conductor is 220V, then what is the potential at the ends and the middle point
.
Answer: As the potential of the earthed point has to be zero therefore the potential of the two ends is 110V and –110V with mid point being at zero potential.

Q.14. Is Gauss law valid for the gravitational fields also?
Answer: Yes gauss law is valid for gravitational field also the only difference being that the constant of
proportionality is changed from 1/4πε0 to G and the charge is replaced by mass ‘m’ inside the Gaussian
surface.

Q.15. Does the positive and negative nature of the potential depends on the nature of test charge?
Answer: No, the potential of the body does not depend on the nature of the test charge. It depends on the
source charge. Generally if the source charge is positive the body is positively charged. If the source
charge is negative the body is negatively charged.

Q.16. Electric field is discontinuous across the surface of the conductor. Is electric potential also
discontinuous there?

Answer: No electric potential is continuous. Electric field may become zero inside it but the electric potential
is constant.

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