The current through the 20-watt lamp connected to a 30-volt source in the parallel circuit is approximately which value?

The current through the 20-watt lamp connected to a 30-volt source in the parallel circuit is approximately which value?

• A. 0.500 A
• B. 0.333 A
• C. 0.667 A
• D. 1.000 A

Answer: (C)

In a parallel circuit, each branch sees the full source voltage, so the lamp’s current is determined by its power rating at that voltage. Use P = V × I, so I = P / V. For a 20-watt lamp at 30 volts, the current is 20 / 30 = 0.666... A, which is about 0.667 A. If you prefer resistance, the operating resistance is R = V^2 / P = 30^2 / 20 = 45 ohms, and then I = V / R = 30 / 45 = 0.667 A. So the current through the lamp is approximately 0.667 A. The other values would correspond to different wattage at the same voltage (for example, 0.5 A would imply 15 W, 0.333 A would imply 10 W, and 1 A would imply 30 W).

In a parallel circuit, each branch sees the full source voltage, so the lamp’s current is determined by its power rating at that voltage. Use P = V × I, so I = P / V. For a 20-watt lamp at 30 volts, the current is 20 / 30 = 0.666... A, which is about 0.667 A.

If you prefer resistance, the operating resistance is R = V^2 / P = 30^2 / 20 = 45 ohms, and then I = V / R = 30 / 45 = 0.667 A.

So the current through the lamp is approximately 0.667 A. The other values would correspond to different wattage at the same voltage (for example, 0.5 A would imply 15 W, 0.333 A would imply 10 W, and 1 A would imply 30 W).