Name__________________________
GS104 Quiz #7
Dr. John Carlson
Show your work.
1. A 120V electric heater draws a current of 25A.
a. What is its resistance?
R = V / I = 120V / 25 A = 4.8Ω
b. How much power does it dissipate?
P = VI = (120V )(25 A) = 3000W
2. You there are two resistors (10Ω - a DVD player - and 20Ω - a TV) in parallel. A 10A
current is flowing through the larger and 20A through the smaller.
a. What is the voltage difference across the resistors?
The voltage difference along a parallel circuit should be the same across
all resistors in parallel.
V = I1 R1 = (10Ω)(20 A) = 200V
V = I 2 R2 = (20Ω)(10 A) = 200V
It checks out.
b. What is the power used by each resistor?
P1 = VI1 = (200V )(20 A) = 4000W
P2 = VI 2 = (200V )(10 A) = 2000W
c. If you were to add a third resistor in parallel to the other two, what would happen
to the overall resistance of the total circuit? Would it increase or decrease?
The total resistance decreases. The voltage stays the same, but the current
increases. Therefore, the total resistance must have decreased to
accommodate the increased current.
3. You have a 2 resistor, series circuit of 5Ω and 10Ω with a 75V source as the supply.
a. What is the total resistance of the circuit?
Rtotal = R1 + R2 = 5Ω + 10Ω = 15Ω
b. What is the current through the circuit?
I total = V / Rtotal = (75V ) /(15Ω) = 5 A