How many amperes will a 28-volt generator be required to supply to a circuit containing five lamps in parallel, three of which have a resistance of 6 ohms each and two of which have a resistance of 5 ohms each?

• A. 1 ampere
• B. 25.23 amperes
• C. 1.11 amperes
• D. 5.0 amperes

Answer: (B)

In a parallel circuit, the voltage across each lamp is the same, and the total current is the sum of the currents in each branch. So find the current in each lamp and add them up.

Current through a lamp is I = V/R. With 28 volts across each lamp:

• Lamps with 6 ohms: each draws 28/6 ≈ 4.6667 A. There are three of them, giving 3 × 28/6 = 14 A total for these lamps.

• Lamps with 5 ohms: each draws 28/5 = 5.6 A. There are two of them, giving 2 × 28/5 = 11.2 A total for these lamps.

Add the branch currents: 14 A + 11.2 A = 25.2 A. Depending on rounding, this is about 25.23 A.

So the generator must supply roughly 25.2 amperes.