Suppose that a parallel plate capacitor is charged to 5000 volts as seen in the photograph below. The power supply is then disconnected for the following experiment. A circular slab of the dielectric phenolic, seen at the bottom of the photograph, is inserted between the two plates of the capacitor. An electric field applied to the dielectric causes it to become polarized, that is, its polar molecules rotate to line up along the electric field lines in the capacitor. What will happen to the voltage across the plates, as measured on the meter, when the dielectric is inserted? After the dielectric is inserted the voltage will be: (1) higher, pinning the meter. (2) lower. (3) the same.

A parallel plate capacitor consists of two equal and oppositely charged metal plates separated by a small distance, as seen in the photograph below. The voltage across the plates that created this charge separation on the plates is measured by the voltmeter in the picture, which is wired across the plates. Now suppose that a thin circular, uncharged metal sheet, with the same diameter as the plates of the capacitor, is inserted between the plates of the capacitor. What happens to the voltage across the plates as measured by the voltmeter when the uncharged metal plate is inserted between the plates of the capacitor? (1) The voltage across the plates will increase. (2) The voltage across the plates will decrease. (3) The voltage across the plates will remain the same.

Example: The capacitor in figure (a) is half-filled with a dielectric, k2 = 2.00, and half filled with air, k1 = 1.00. What fraction of the capacitor in figure (b) must be filled with the same dielectric to have the same capacitance as in figure (a)? The plates of capacitor have an area A and a separation distance d. Figure (a): Resembles two capacitors in parallel. d4

Figure (b): Resembles two capacitors in series. 4

A nickel is balanced on its edge in the center of a piece of paper, and a wooden match is balanced on the nickel. A plastic cup is placed upside down over the nickel and match, and a second nickel is balanced on bottom of the upside-down cup. This is shown in the photograph below. To dislodge the matchstick without overturning either of the two nickels as seen in the photograph, you must: (1) move the paper out from under the cup. (2) move one pole of a magnet near the cup. (3) move a charged rod near the cup.