How many bulbs are in a 120-volt circuit according to the calculation?

How many bulbs are in a 120-volt circuit according to the calculation?

• A. 5 bulbs
• B. 10 bulbs
• C. 20 bulbs
• D. 15 bulbs

Answer: (D)

In a circuit where identical bulbs are placed in series, the total supply voltage is divided among all the bulbs, with each bulb dropping a portion of that voltage. The number of bulbs you can connect in series on a 120-volt supply is found by dividing the total voltage by the voltage drop of a single bulb. Here, each bulb is assumed to drop 8 volts. So 120 volts ÷ 8 volts per bulb = 15 bulbs. That’s why the calculation yields fifteen bulbs as the result. Keep in mind that in typical home wiring, lights are wired in parallel so each one sees the full 120 volts, but this question uses a series assumption to illustrate how voltage adds up across identical components. If the bulbs dropped a different voltage, the count would change accordingly (for example, 120 ÷ 10 = 12 bulbs, 120 ÷ 12 = 10 bulbs, etc.).

In a circuit where identical bulbs are placed in series, the total supply voltage is divided among all the bulbs, with each bulb dropping a portion of that voltage. The number of bulbs you can connect in series on a 120-volt supply is found by dividing the total voltage by the voltage drop of a single bulb.

Here, each bulb is assumed to drop 8 volts. So 120 volts ÷ 8 volts per bulb = 15 bulbs. That’s why the calculation yields fifteen bulbs as the result.

Keep in mind that in typical home wiring, lights are wired in parallel so each one sees the full 120 volts, but this question uses a series assumption to illustrate how voltage adds up across identical components. If the bulbs dropped a different voltage, the count would change accordingly (for example, 120 ÷ 10 = 12 bulbs, 120 ÷ 12 = 10 bulbs, etc.).