PHYSICS
Name ________________________#______
CH 22/23:
Ohm’s Law ws2
Period _______Date _________
1. An automobile panel lamp with a resistance of 33 Ω is placed across a 12-V battery. What is the
current through the circuit?
V=IR
12 V = I(33Ω)
I=0.36 A
2. A sensor uses 2.0x10​-4​ A of current when it is operated by a 3.0-V battery. What is the resistance
of the sensor circuit?
V=IR
3.0 V = (2.0 X 10​-4​ A)R
R = 1.5 X 10​4​ Ω or 15 kΩ
3. A 75-W lamp is connected to 125 V.
a. What is the current through the lamp?
P=IV
75 W = I(125 V)
I=0.60 A
b. What is the resistance of the lamp?
V=IR
125 V=(0.60 A)R
R=210Ω
4. A resistor is added to the lamp in the previous problem (#3) to reduce the current to half of its
original value.
a. What is the potential difference across the lamp?
I is half , 0.60 A X 0.5 = 0.30 A
V=IR
= (0.30 A)(210 Ω)
=63 V
b. How much resistance was added to the circuit?
125 V - 63 V = 62 V
62 V = (0.30 A)R
R = 210 Ω
c. How much power is now dissipated in the lamp?
P = IV
= (0.30 A)(63 V)
= 19 W
5. Sue finds a device that looks like a resistor. When she connects it to a 1.5-V battery, she
measures only 45x10​-6​ A, but when she uses a 3.0-V battery, she measures 25x10​-3​ A. Does the
device obey Ohm’s law?
V=IR
3.0 V=(25 X 10​-3​ A)R
1.5 V=(45 X 10​-6​ A)R
R=120Ω
R=3.3 X 10​4​ Ω
No, it does not obey Ohm’s Law because the resistances are different.