Download Suppose two charges, q and 3q, are placed 3

Semester 2 Test 1 Study Guide
Resistors tend to have large units and Capacitors tend to have small units. Makes
sure you know all of your metric prefixes from pico - Giga
1. Suppose two charges, q and 3q, are placed 3.39 m apart. If the magnitude of the
electric force between the charges is 2.4 x10-6 N, what is the value of q?
2. Suppose two charges, +1 C and -3 C, are placed 3.39 m apart.
a. Find the magnitude of the electrostatic force?
b. Is it attractive of repulsive?
c. What is the imbalance of protons & electrons on the -3 C charge?
d. Are there more protons or electrons?
3. Consider a group of 4.00 x103 protons and a group of 3.20 x105 electrons that are
1.00 km apart. Calculate the magnitude of the electric force between them.
4. Calculate the magnitude of the electric force if the number of protons is increased to
3.20 x105 particles and the separation distance remains the same.
5. An electric field of 9.0 N/C is directed along the positive x-axis. What is the electric
force on a –6.0 C charge in this field? (F=qE)
6. Millikan’s experiment measures the charge of an electron by suspending charged oil
droplets in an electric field. If an oil droplet with a mass of 3.35 x10-15 kg has the
same charge as an electron what electric force is required to balance the weight of
the oil droplet?
7. An electric field of 4.0 x103 N/C is directed downward. If the electric force on a
charge is 6.43 x10-19 N, what is the charge?
8. After brushing your hair many times, you notice that your hair is attracted to the
brush. Suppose a charge of +64 nC is on the brush and a charge of 64 nC is on your
hair.
a. How many electrons were transferred?
b. What direction did the electrons move?
9. Suppose you would like to develop a hat that wouldn’t fall off someone’s head by
putting enough charge on the hat so that it would stay no matter how much the wind
blew. You begin by rubbing a silk hat against your head so that the same amount of
charge collects on the hat as the charge on your head. When you wear the hat (r =
1.25 x 10-3 m), the force associated with the hat and your head is 1.25 x 10-4 N. The
hat stays as you walk into the wind.
a. How much charge was on the hat?
b. How much charge was on your head?
c. Suppose your friend approaches and puts the hat on. Is the hat likely to stay
on your friend’s head by charge alone?
d. Why or why not?
10. A 10 Ω resistor, a 12 Ω resistor, a 15 Ω resistor and an 18 Ω resistor are connected
in parallel across a potential difference of 12 V. What is the equivalent resistance?
11. Polyester capacitors can have a capacitance of 5.0 x 10-5 F. What potential difference
is required to store 6.0 x 10-4 C?
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17.
Draw the electric field around:
2 positive charges
2 negative charges
1 positive & 1 negative charge
a single proton
a single electron
18. For training purposes an astronaut is being floated between two metal plates by an
electric field. If the mass of the astronaut is 3.0x102kg and the charge on it is 3.0x102
C, how strong is the electric field? (Include a Pic., FBD and Units)
19. A capacitor has a capacitance of 120 µF and is plugged into a wall socket that gives
out 120 V of potential. Find the charge stored on the capacitor.
20. Write everything you know is true about a series circuit.
21. Write everything you know is true about a parallel circuit.
22. The current through a light bulb in a flashlight is 0.750 A.
How much charge passed through the filament
a. in 20.0 s?
b. in 5.00 min?
c. in 2.00 h?
23. The motor of a garbage disposal has a resistance of about 25.0 Ω. If the current
through the motor equals 4.66 A, what is the potential difference across the motor’s
terminals?
24. A washing machine motor carries a current through a circuit with a resistance of 12.2
Ω. If the washing machine is plugged into a 120 V outlet, what is the current in the
motor?
25. If the potential difference across the car’s motor is 720 V and the resistance was 0.30
Ω, how much power was needed for the car to run?
26. A microwave oven requires 1750 W of power to cook food. If the oven is plugged
into a
120 V outlet, what is the resistance in the oven’s circuit?
27. A bread machine requires 1200 W to bake bread. How much time is required for it
to use 1.512 x1010 J of energy?
28. Suppose you receive an electric bill which states the following:
Final Meter Reading 24422 kWh
Previous Meter Reading 24204 kWh
Rate = $0.078/kWh
How much must you pay the electric company?