AS Daily A Level Physics question
An ideal 6 V bench supply powers one identical 6 V filament lamp. A second, identical lamp is then connected in parallel across the same supply using identical leads. Ignore lead resistance and assume the supply voltage stays at 6 V. Which statement must be true after the second lamp is added?
Answer
The correct answer is D.
Correct: D — Each lamp's brightness is unchanged, and the power drawn from the supply doubles because the total current doubles. A Each lamp still has the full 6 V in parallel, so brightness (power per lamp) does not drop, and with two identical branches the total current doubles, so total power does not stay the same. B A higher total current does not make each parallel lamp brighter when the voltage across each is fixed; and power from the supply does not halve when adding a second identical load. C Although the supply voltage is the same, the equivalent resistance halves with two identical parallel branches, so total current and thus total power both double; it is not unchanged. D With two identical lamps in parallel, each still has 6 V so each lamp’s power (and brightness) is the same as before, while the total current is twice the single-lamp current, so supply power (V × I_total) doubles.