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Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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# Four 12-V 18-W light bulbs are connected in series. What is

### Customer Question

Four 12-V 18-W light bulbs are connected in series. What is the total power and the total resistance?
Submitted: 10 months ago.
Category: Electrical
Expert:  Kevin replied 10 months ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) Since each light bulb is 12 volts and there are a total of 4 bulbs, the circuit source voltage = 12V x 4 = 48 volts.

2) Each bulb = 18 watts and each bulb has a voltage drop of 12 volts, solve for current (I). Apply Ohms Law where I = P/E. I = 18W/12V = 1.5 amps = total circuit current.

3) Next solve for Total Power by applying Watts Law where P = I x E. P = 1.5 amps x 48 volts = 72 total watts. Check by adding each of the four 18 watt light bulbs (18+18+18+18) = 72 total watts or total power.

4) Next, solve for the individual resistance on each light bulb by applying Ohms Law where R = E/I. Since each bulb is 12 volts and a series current of 1.5 amps in the circuit, R = 12/1.5 = 8 ohms each light bulb. Since a total of four light bulbs in the circuit, the total circuit resistance = 8 x 4 = 32 ohms.

Check if 32 ohms is correct by applying Ohms Law where I = E/R. Solve for total circuit voltage. E = I x R = 1.5 X 32 ohms = 48 volts. Therefore, the total circuit resistance = 32 ohms.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks...............Kevin:)

Expert:  Kevin replied 10 months ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks...............Kevin:)

Expert:  Kevin replied 10 months ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks................Kevin:)

Expert:  Kevin replied 10 months ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.

Thanks..................Kevin:)