In a simple parallel circuit with two identical bulbs, how does their brightness compare?

In a simple parallel circuit with two identical bulbs, how does their brightness compare?

• A. They have equal brightness
• B. The first bulb is brighter
• C. The second bulb is brighter
• D. One is on and one is off

Answer: (A)

Brightness is determined by the power each bulb dissipates. In a parallel circuit, each bulb is directly across the supply, so each branch has the full supply voltage. If the bulbs are identical, they have the same resistance. The power for a bulb is P = V^2 / R, so each bulb dissipates the same amount of power. Because brightness correlates with power, both bulbs glow equally bright. The total current drawn is the sum of the currents in each branch, but that doesn’t change the brightness of either bulb since each still sees the same voltage.

Brightness is determined by the power each bulb dissipates. In a parallel circuit, each bulb is directly across the supply, so each branch has the full supply voltage. If the bulbs are identical, they have the same resistance. The power for a bulb is P = V^2 / R, so each bulb dissipates the same amount of power. Because brightness correlates with power, both bulbs glow equally bright. The total current drawn is the sum of the currents in each branch, but that doesn’t change the brightness of either bulb since each still sees the same voltage.