Question

What happens when a second bulb is added to a circuit,do the bulbs glow dimmer?

Answer 1

Maybe.

Explanation:

This depends on the connectivity of the circuit: specifically, whether the bulbs are connected in parallel or in series .

In the case that the current available to the system is not restricted (e.g. you are powering the circuit with a battery which can put out more or less current): if two bulbs are connected in parallel, the voltage across the bulbs will be equal to the voltage of the battery. If the two bulbs are connected in series, there will be a lower voltage across each of the bulbs.

Ohm's law gives `V=IR`, and so we expect to have more current running through the bulbs connected in parallel.

Because the brightness of the bulb depends on the current running through it, we conclude that two bulbs connected in parallel burn brighter than two bulbs connected in series for otherwise the same circuit.

The answer to your question, then, is yes for a connection in series, and no for a connection in parallel.