Physics 110
Physical Science
Name _______________
Date ________________
Exercise 11: Electricity and Magnetism
1. A student lamp with a 60-W light bulb is plugged into a 120-V wall outlet.
a. What is the current through the lamp?
P = IV  I = P/V = 60/120 = 0.50 A
b. What is the resistance of the lamp?
Ohm’s Law V = IR  R = V/I = 120/0.50 = 240 Ω
2. A coffee cup immersion heater utilizes a heating coil with a resistance of 8.5 Ω.
a. Determine the current through the coil when operated at 120 V.
Ohm’s Law V = IR  I = V/R = 120/8.5 = 14.1 A
b. What is the power consumption?
P = IV = (12.9)(120) = 1690 W
3. Two 30-Ω resistors are connected in series to a 10-V battery.
a. Draw a schematic showing the battery and resistors.
b. What is the equivalent resistance?
Series Req = R1 + R2 = 30 + 30 = 60Ω
c. What is the current in the first resistor?
V = IR  I = V/Req = 10/60 = 0.17 A
4. Two 30-Ω resistors are connected in parallel to a 10-V battery.
a. Draw a schematic showing the battery and resistors.
b. What is the equivalent resistance?
Parallel 1/Req = 1/R1 + 1/R2 = 1/30 + 1/30 = 2/30 = 1/15
Req = 15 Ω
5. A pole –mounted transformer is designed to step down a voltage from
7,200 V to 120 V. If the primary side has 10,000 coils, approximately how
many should there be on the secondary side?
Transformer Equation V1/V2 = N1/N2
 N2 = N1 (V2/V1) = 10,000 (120/7,200) = 167 coils
1