Wed April 18, 2012 By: Samuel Roy

A large number of light bulbs are to be connected to a single electrical outlet in which case the bulb will provide more brightness in series or in parallel

Expert Reply
Thu April 19, 2012

A series circuit can be constructed by connecting light bulbs in such a manner that there is a single pathway for charge flow; the bulbs are added to the same line with no branching point. As more and more light bulbs are added, the brightness of each bulb gradually decreases. This observation is an indicator that the current within the circuit is decreasing.

So for series circuits, as more resistors are added the overall 
current within the circuit decreases. This decrease in current is consistent with the conclusion that the overall resistance increases.

The diagrams below depict the usual means of constructing the circuit with parallel connections of light bulbs. One will note that a study of the overall current for parallel connections requires the addition of an indicator bulb. The indicator bulb is placed outside of the branches and allows one to observe the affect of additional resistors upon the overall current. The bulbs that are placed in the parallel branches only provide an indicator of the current through that particular branch. So if investigating the affect of the number of resistors upon the overall current and resistance, one must make careful observations of the indicator bulb, not the bulbs that are placed in the branches. The diagram below depicts the typical observations.

It is clear from observing the indicator bulbs in the above diagrams that the addition of more resistors causes the indicator bulb to get brighter. For parallel circuits, as the number of resistors increases, the overall current also increases. This increase in current is consistent with a decrease in overall resistance. Adding more resistors in a separate branch has the unexpected result of decreasing the overall resistance!

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