Physics Multiple Choice Questions on “Equipotential Surfaces”.
1. What is the nature of equipotential surfaces in case of a positive point charge?
a) Circular
b) Spherical
c) Cubical
d) Cylindrical
Answer: b
Clarification: We know that electric field lines cross the equipotential surfaces perpendicularly. Electric field lines are generated radially from a positive point charge. Therefore, for holding both the conditions, the equipotential surfaces must be spherical.
2. What will be the nature of equipotential surfaces due to a point charge, situated at infinity?
a) Plane surface
b) Spherical
c) Elliptical
d) Cylindrical
Answer: a
Clarification: If a point charge is situated at infinity, the electric field lines coming out of it will be in the form of parallel straight lines. As we know that field lines cut the equipotential surfaces orthogonally, therefore the equipotential surfaces must be plane surfaces. They can be considered the surface of a sphere of infinite radius.
3. An electric field is directed along the tangent of an equipotential surface.
a) True
b) False
Answer: b
Clarification: Electric field lines cut the equipotential surfaces at an angle of 90 degrees. The direction of the electric field is the same as the direction of electric field lines. Therefore, the field is perpendicular to the equipotential points, not tangent to them.
4. Which of the following statements is correct?
a) An electric field is a scalar quantity
b) Electric field lines are at 45 degrees to the equipotential surfaces
c) The surface of a charged conductor is equipotential
d) Field lines due to a point charge are circular
Answer: c
Clarification: In conductors, charges are equally distributed over the surface of the conductor. Therefore the potential throughout the surface is the same, i.e. equipotential. The electric field is a vector quantity and the field lines cut the equipotential surfaces at 90 degrees. The field lines due to a point charge are radial.
5. A charge q is placed on an equipotential surface and electric field intensity at that place is E. What is the work done to move the charge by a distance x on the surface?
a) x*(frac {q}{E})
b) x*q*E
c) E*(frac {x}{q})
d) Zero
Answer: d
Clarification: As the surface is equipotential, all the points on the surface of the plane have the same potential values. Therefore work done to move the charge by a distance x on that surface is zero. The electric field plays no role here.
6. A smaller sphere has potential 50V and a larger sphere has potential 100V. How should they be placed so that if they are connected with the help of a wire, the charge will flow from the smaller sphere to the larger sphere? Both the spheres are conducting and hollow.
a) Concentrically
b) Touching each other
c) It is never possible
d) The smaller sphere should be grounded
Answer: a
Clarification: We know that for a conducting sphere, the charge is always distributed on its outer surface. We also know that charge flows from higher potential to lower potential. But if we put the smaller sphere inside the larger sphere and connect them with a conductor, they will act as a single conductor and charge will be distributed to its outer surface, i.e. charge will flow to the larger sphere.