AT 121 – Lab 2 – Ohms Law – Chapter 2 – Part 1 -
ANSWER KEY
Name :__________________________________
Date: ___________________________________
After completing this lab you will be able to:
Explain the Relationship between voltage, current, and resistance
Determine current flow, resistance, and voltage in a circuit given only two values of that given circuit
Calculate the voltage drop across a load
An understanding of how resistance affects voltage and current will help you understand and trouble shoot
automotive electrical circuits by explaining what values you should get while using a DVOM. This will help you
diagnose automotive electrical problems quicker and more accurately.
1. Ohm's Law states that...
A.
B.
C.
D.
Voltage = Current x Resistance
Voltage = Resistance / Current
Current = Voltage x Resistance
Resistance = Current x Voltage
2. In an electrical circuit, if the voltage stays the same, but the resistance increases, the current will...
A.
B.
C.
D.
Increase
Increase or decrease, depending on the amount the resistance goes up
Decrease
Stay the same
3. To find the amount of Watts in a circuit you would;
A.
B.
C.
D.
Watts = Volts x Current
Watts =Voltage x Resistance
Watts =Current x Resistance
Watts = Volts / Current
4. What would happen if a 5A fuse were in place of a 30A Fuse?
A.
B.
C.
D.
The fuse would blow
The circuit would be damaged
The component that the fuse is protecting would be damaged
Choice B and C
5. What would happen if a 30A fuse were in place of a 5A Fuse?
A.
B.
C.
D.
The fuse would blow
The circuit would be damaged
The component that the fuse is protecting would be damaged
Choice B and C
6. Draw the formula for Ohm’s Law –
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7. Draw the formula for Watt’s Law –
8. Show the formula for finding total resistance in a parallel circuit with two resistors.
9. Show the formula for finding total resistance in a parallel circuit with three resistors.
10. Show the formula for finding total resistance in a series circuit with 4 resistors.
11. If corroded switch terminals caused abnormal, increased resistance at a switch, the total current flow
in a circuit would...
A.
B.
C.
D.
Increase or decrease, depending on the amount of resistance increase
Increase
Decrease
Stay the same
12. If shorted switch terminals caused abnormal, decreased resistance at a switch, the total current flow
in a circuit would...
A.
B.
C.
D.
Increase or decrease, depending on the amount of resistance increase
Increase
Decrease
Stays the same
13. A technician is installing an amplifier in a vehicle. The vehicle's amplifier is a 400-Watt Amp. If the car's
peak voltage is 15 Volts, how big of a fuse must be wired on to the sub?
26.666666 A
Or 30 A
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14. The circuit to the right shows:
A.
B.
C.
D.
A Series Circuit
A Parallel Circuit
An open Circuit
A Series Parallel Circuit
15. Find the total resistance in the circuit to the right;
If “X” Ohms were and
If “Y” Ohms were =
A. 6 Ohm
9 Ohms = ________15________________
B. 20 Ohms
30 Ohms = _______50_________________
C. 40 Ohms
400 Ohms = _____440_______________
D. 1 Ohm
1 Ohm = ___________2_____________
E. 4 Ohms
900 Ohms = ________904_______________
F. 1 Ohms
7 Ohms = ____________8____________
16. Given the above values, find the total current flow = I = V/R
A. ________0.8_________
B. ________.24__________
C. ______.0272727___________
D. _______6_________
E. 0.013274336
F. ________1.5________
17. Given the above values, find the voltage drop for Ohm “X”
(Hint! Use Ohm’s Law! You know total current, and the resistance of on of the bulbs! Find Voltage!)
A. ______4.8
_______
B. _______4.8_________
C. _______1.08 _______
D. ______6
_________
E. ______ 0.05308_______
F. _______1.5________
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18. The circuit to the right shows:
A.
B.
C.
D.
A Series Circuit
A Parallel Circuit
An open Circuit
A Series Parallel Circuit
19. Find the total resistance in the circuit to the right;
If “X” Ohms were and
If “Y” Ohms were =
A. 6 Ohm
9 Ohms = ________ 3.6_____________
B. 20 Ohms
30 Ohms = ________ 12_____________
C. 40 Ohms
400 Ohms = _______ 36.364____________
D. 1 Ohm
1 Ohm = ________ 0.5___________
E. 4 Ohms
900 Ohms = _____ 3.9823__________
F. 1 Ohms
7 Ohms = _______ 0.875___________
20. Given the above values, find the total current flow -= Calculate Current I=V/R
A. _____3.333________
B. ________1_________
C. 0.329996700032999670
D. _______24________
E. 3.01333400296311176
F. 13.71428571428571428
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21. The circuit to the right shows:
A.
B.
C.
D.
A Series Circuit
A Parallel Circuit
An open Circuit
A Series Parallel Circuit
22. Find the total resistance in the circuit from question 19.
If “X” Ohms were and
If “Y” Ohms were and
If “Z” Ohms were = Total Resistance
A. 6 Ohm
9 Ohms
10 Ohms
= ________ 2.6471___________
B. 20 Ohms
30 Ohms
40 Ohms
= _____ 9.2308__________
C. 40 Ohms
400 Ohms
2 Ohms
= _________ 1.8957_________
D. 1 Ohm
1 Ohm
.5 Ohms
= _________ 0.25_________
E. 4 Ohms
900 Ohms
1000 Ohms
= _______ 3.9665__________
F. 1 Ohms
7 Ohms
5 Ohms
= _______ 0.74468___________
23. Given the above values, find the total current flow
A. ______4.5_______
B. ____1.29999__________
C. ______6.3301_________
D. ______48________
E. 3.0253371990419
F. 16.114304130633
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24. The circuit to the right shows:
A.
B.
C.
D.
A Series Circuit
A Parallel Circuit
An open Circuit
A Series Parallel Circuit
25. Find the total resistance in the circuit from question 21. MAKE SURE YOU SOLVE 20 and 21 first!
(Hint! Calculate the parallel Curtis first, then add up the rest of the resistors that make it a series circuit!)
If “X” Ohms were and
If “Y” Ohms were and
If “Z” Ohms were and 1 Ohm = Total Resistance
A. 6 Ohm
9 Ohms
10 Ohms
= ________________________
B. 20 Ohms
30 Ohms
40 Ohms
= ________________________
C. 40 Ohms
400 Ohms
2 Ohms
= _______________________
D. 1 Ohm
1 Ohm
.5 Ohms
= ________________________
E. 4 Ohms
900 Ohms
1000 Ohms
= _______________________
F. 1 Ohms
7 Ohms
5 Ohms
= ________________________
26. Given the above values, find the total current flow
A. __________________
B. ____________________
C. ____________________
D. __________________
E. ____________________
F. ____________________
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