Physics - Parallel circuits
A parallel circuit  is defined as one in which there are alternative
paths for the flow of electricity. In the circuit shown, any coulomb of
charge leaving the battery will either pass through one load OR the other.
It cannot pass through both loads. The voltage provided by the battery must
be fully used by that one load item. Hence
The current path is divided and a portion of the total current flows
through each load. Since current is defined as the number of coulombs of
charge past a given point per second, the sum of the current in each branch
of the circuit must equal the total current in the circuit. Note that the
current coming out of the supply must be equal to the current returning to
Since the current has alternative paths that it can take, any coulomb of
charge will only flow through one load. With any two particular load
resistances, the result of constructing a parallel circuit rather than a
series circuit is that the total circuit resistance will be considerably
less. The total resistance of a parallel is given by:
Some circuits involve a combination of items connected in parallel with
one another, then connected in series with other items. Wherever
appropriate, calculate the resistance of the parallel part of the circuit
first and treat this as being in series with the other items.
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