Question
A parallel plate capacitor with air between the plates is charged and then disconnected from the source of emf. If the space between the plates is now filled with a dielectric, what happens to the
capacitance of the capacitor and the magnitude of the electric field between the plates?
Capacitance Magnitude of the Electric Field
(A) Increases Increases
(B) Increases Remains constant
(C) Increases Decreases
(D) Decreases Increases
(E) Decreases Decreases
Answer/Explanation
Question
The figure above shows a cross section of two concentric spherical metal shells of radii R and 2.R, respectively. Find the capacitance.
(A) 1/(8πεoR)
(B) 1/(4πεoR)
(C) 2πεoR
(D) 4πεoR
(E) 8πεoR
Answer/Explanation
Ans:E
Along the line joining the two charges of an electric dipole, the individual electric field vectors point in the same direction, so they add constructively. At the point equidistant from both charges, the total electric field vector has magnitude
\(E_{+}+E_{-}=2E=2\frac{kQ}{(\frac{1}{2}d)^{2}}=\frac{8kQ}{d^{2}}\)
\(=\frac{8(9\times 10^{9}N.m^{2}/C^{2})(4.0\times 10^{-9}C)}{(2.0\times 10^{-2}m^{2})^{2}}\)
= 72 x l04 N/C
=7.2 x l05
Question
Two large oppositely charged parallel plates are initially separated by a distance d. The uniform electric field between the plates has magnitude E. Next, the magnitude of the charge on each plate
is doubled, while the separation distance d is doubled. What is the new electric field magnitude?
(A) E
(B) E/4
(C) E/2
(D) 4E
(E) 2E
Answer/Explanation
Ans:E
Question
A parallel plate capacitor consists of identical rectangular plates of dimensions a × b, separated by a distance c. To cut the capacitance of this capacitor in half, which of these quantities should be doubled?
(A) a
(B) b
(C) c
(D) ab
(E) abc
Answer/Explanation
Ans:C
Capacitance of a parallel-plate capacitor is εo
Question
A battery or batteries connected to two parallel plates produce the equipotential lines between the plates shown
above.
Which of the following configurations is most likely to produce these equipotential lines?
Answer/Explanation
Ans: D
The potential difference between the plates is 4V, this can be produced with two 2V batteries in