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Kevin, Licensed Electrician

Category: Electrical

Satisfied Customers: 3107

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?

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.

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