Question

You connect a number of identical light bulbs to a flash-light battery.

(a) What happens to the brightness of each bulb as more and more bulbs are added to the circuit if you connect them (i) in series and (ii) in parallel?

(b) Will the battery last longer if the bulbs are in series or in parallel? Explain your reasoning.

Short answer

1. (i) The brightness will be reduced.

(ii) The same brightness.

b. In a series connection, the battery last longer.

Step-by-step solution

Definition of series and parallel connection

In a series circuit, all components are connected in a pattern where the second end of one component is connected to the first end of another component.

In a parallel circuit, all components are connected across each other, and they have the same potential drop at the common points.

Determining the brightness of each bulb connected in series and parallel

a)

Here, the voltage of the battery will not be changed.

1. In series, the resistance will increase as the number of bulbs increases, therefore, the current through each bulb will decrease and the brightness will be reduced as the current decreases.
2. In parallel, the voltage is the same across each bulb and as the number of bulbs increases, the voltage will be the same for each bulb, therefore the bulbs will keep the same brightness.

Reasoning for the battery to last longer if connected in series or parallel

b)

In parallel, the total current is the sum of the individual current in each bulb and the voltage drop is the same across each bulb. Therefore, more energy is consumed to keep the brightness of the bulbs. So, in a series connection, the battery last longer.

Thus, the brightness will be reduced in a series connection, and it remains the same in a parallel connection. In a series connection, the battery last longer.