Multiple Choice Problems-put correct answer on front page
Consider a parallel plate capacitor connected to a battery that maintains the plates at a potential
V and a slab of dielectric with the same area and with thickness equal to the gap
between the plates. Which of the following is a true statement regarding the situation as the
dielectric is inserted into the capacitor at small constant velocity by some external force?
The absolute magnitude of the work done by the battery is equal to the absolute magnitude of the
work done by the force that is moving the dielectric in at constant velocity.
No, since total work
is not zero, and the work or battery is opposite in sign to that of the external force.
The energy stored in the battery decreases during the process of inserting the dielectric.
The work done by the external force is negative.
Yes, the plate is pulled in by electric force, and
the external force is against the displacement.
Exactly 2 of the above statements
Two conducting plates of area A are parallel to each other and separated by a distance d, with
, so edge effects can be ignored. If each plate has a charge Q on it, what is the magnitude of
the force one plate exerts on the other?
Field of one sheet at the other is Q/2A
charge is Q
none of the above
Consider two charges, each of magnitude Q, at (x,y) = (1,0),
and (0,1). Which of the following
charges, when added at the indicated position, would result in a field at the origin equal to zero?
2Q at (-1 , -1)
2Q at (-
Q at (-1,-1)
–Q at (-1,-1)
none of the above
Magnitude of original E is kQ/(1
), none of these cancels that field.
Assuming that 3 charges (Q,Q,-2Q) start very far from each other, how much work must be done by
an external force to make a configuration with Q fixed at (a,0,0), Q at (0,a,0) and -2Q at (0,0,a)?