AT 121 – Lab 2 – Ohms Law



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. Voltage = Current x Resistance

B. Voltage = Resistance / Current

C. Current = Voltage x Resistance

D. Resistance = Current x Voltage

2. In an electrical circuit, if the voltage stays the same, but the resistance increases, the current will...

A. Increase

B. Increase or decrease, depending on the amount the resistance goes up

C. Decrease

D. Stay the same

3. To find the amount of Watts in a circuit you would;

A. Watts = Volts x Current

B. Watts =Voltage x Resistance

C. Watts =Current x Resistance

D. Watts = Volts / Current

4. What would happen if a 5A fuse were in place of a 30A Fuse?

A. The fuse would blow

B. The circuit would be damaged

C. The component that the fuse is protecting would be damaged

D. Choice B and C

5. What would happen if a 30A fuse were in place of a 5A Fuse?

A. The fuse would blow

B. The circuit would be damaged

C. The component that the fuse is protecting would be damaged

D. Choice B and C

6. Draw the formula for Ohm’s Law –

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. Increase or decrease, depending on the amount of resistance increase

B. Increase

C. Decrease

D. Stay the same

12. If shorted switch terminals caused abnormal, decreased resistance at a switch, the total current flow

in a circuit would...

A. Increase or decrease, depending on the amount of resistance increase

B. Increase

C. Decrease

D. 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

14. The circuit to the right shows:

A. A Series Circuit

B. A Parallel Circuit

C. An open Circuit

D. 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________

18. The circuit to the right shows:

A. A Series Circuit

B. A Parallel Circuit

C. An open Circuit

D. 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

21. The circuit to the right shows:

A. A Series Circuit

B. A Parallel Circuit

C. An open Circuit

D. 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

24. The circuit to the right shows:

A. A Series Circuit

B. A Parallel Circuit

C. An open Circuit

D. 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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