1. Sep 5, 2004

### rosely

Electric Potential energy and the electric potential:
10) a spark plug in a car has electrodes separated by a gap of 0.025 in. To create a spark and ignite the air-fuel mixture in the engine, an electric field of 3.0 * 10^6 V/m is required in the gap.
a) what potential difference must be applied to the spark plug ti initiate a spark?
b) if the separation between electrodes is increased, does the required potential difference increase, decrease, or stay the same ? explain.
c) Find the potential difference for a separation of 0.050in.

Electric potential of point charges:
25) Point charges +4.1uC and -2.2uC are placed on the x-axis at (11m, 0) and (-11m, 0), respectively.
a) Sketch the electric potential on the x-axis for this system.
b) Your sketch shoul show onw point on the x-axis between the two charges where the potential vanishes. Is this point closer to the +4.1uC charge or closer to -2.2uC charge? Explain
c) Find the point referred to in part (b).

32) How much work must be done to move the three charges in figure 20-23 infinitely far from one another?

Equipotential Surfaces and the Electric Field;
36) two point charges are on the x-axis. Charge 1 is +q and is located at x=-1.0m, charge 2 is -2q and is located x=1.0m. Make sketchs of the equipotential surfaces for this system.
a) out to a distance of about 2.0m from the origin.
b) far from the origin. in each case, indicate the direction in which the potential increases.

Capacitors and Dielectrics
47) A parallel-plate capacitor has plates of area 3.45*10^ -4 m^2. What plate separetion is required if the capacitance is to be 1330 pF? Assume that the space between the plates if filled with
a) air
b) paper

Electrical Energy Storage
59) an electronic flash unit for a camera contains a capacitor with a capacitance of 850 uF. when the unit is fully charged and ready for operation the potential difference between the capacitor plates is 330 V.
a) what is the magnitude of the charge on each plates of the fully charged capacitor?
b) Find the energy stored in the " charged-up" flash unit.

thanks