Compare a series circuit with two bulbs to a series circuit with four bulbs. how would you expect the brightness of the two bulb circuit to compare to the brightness of the four bulb circuit?
a. all of the bulbs would be equally bright.
b. the bulbs in the two bulb circuit would be brighter than those in the four bulb circuit.
c. the bulbs in the four bulb circuit would be brighter than those in the two bulb circuit.
d. none of the bulbs would light in either circuit.

B. the bulbs in two bulb circuit would be brighter than those in the four bulb circuit. 

this is because in a series circuit, as we increase the number of bulbs in it, the total resistance of the circuit also increases, and since current is inversely proportional to resistance, as resistance increases, the current across it decreases. hence, the series circuit with only two bulbs have less resistance across it than a series circuit with 4 bulbs, meaning that bulbs in two bulb circuit will be brighter than those in four bulb circuit