physics 79

Week 1 –
Electric Charges, Fields and Potentials
Please solve the following problems. You must show all work for full/partial credit. When complete, attach a typed cover sheet and submit to the assignment drop-box.
1) An electron that is a certain distance from a proton is acted on by an electrical force.
a) If the electron were moved twice the distance away from the proton, would the electrical force be:
1) 2
2) ½
3) 4
4) ¼
b) If the initial electric Force is, F, and the electron were moved to one third he original distance toward the proton, what would be the new electrical force?
2) What is the magnitude and direction of the electric field at a point 0.75 m away from a point charge of +2.0 pC?
3) Two fixed charges -4.0  C and -5.0  C, are separated a certain distance.
a) Is the net electric field at a location halfway between the two charges:
1) directed toward the -4.0  C charge
2) Zero
3) directed toward the -5.0  C charge
b) If the charges are separated by 20 cm, calculate the magnitude of the net electric field halfway between the two charges.
4) What is the speed of a proton whose kinetic energy is 12.9 keV?
5) An electron is accelerated by a uniform electric field (1000 V/m) pointing vertically upward. Use energy methods to get the magnitude and direction of its velocity after it moves 0.10 cm form rest. Does the electron gain or lose potential energy?
6) How much charge flows through a 12 –V battery when a 2.0 mF capacitor is connected across its terminals?
Week 2 –
Electric Current and Circuits
Please solve the following problems. You must show all work for full/partial credit. When complete, attach a typed cover sheet and submit to the assignment drop-box.
1) How long would it take for a net charge of 2.5 C to pass a location in a wire if it is to carry a steady current of 5.0 mA?
2) Two copper wires have equal lengths, but the diameter of one is three times that of the other.
a) The resistance of the thinner wire is _____ times that of the thicker wire: (Prove your work)
1) 3
2) 1/3
3) 9
4) 1/4
b) If the t wire has a resistance of 1.0  , what is the resistance of the thinner wire?
3) A 200 – W computer power supply is on 10 hours per day. If the cost of electricity is $0.15/kWh, what is the cost (to the nearest dollar) to run the computer every day for a year (365 days)?
4) What is the emf of a battery with an internal resistance of 0.15   if the battery delivers 1.5 A to an externally connected 5.0  resistors?
5) Three resistors of value 1.0  , 2.0  and 4.0  are connected in a parallel circuit with a 6.0 V battery.
a) What is the total equivalent resistance?
b) What is the across each resistor?
c) The power delivered to the 4.0  resistor?
6) What is the equivalent capacitance of two capacitors of 0.40  F and 0.60  F when they are connected in:
a) series?
b) parallel?
7) Three capacitors of equal capacitance are connected in parallel to a battery, and together they draw a certain amount of charge Q from that battery.
a) Will the charge on each capacitor be
1) Q
2) 3Q
3) Q/3?
b) Three capacitors of 0.25  F each in parallel connected to a 12- V battery. What is the charge on each capacitor?
c) How much charge is drawn from the battery?
Week 3 –