Download Series and Parallel Circuits 1 - Analysis

Voltage and Current
UM Physics Demo Lab 07/2013
Current and voltage are the two quantities used to describe the behavior of electricity in
a circuit.
Voltage
The total electric potential (“voltage”) across a circuit cannot exceed the voltage of the
power source (battery). The power source provides stored electrical energy ready to
power a circuit. Voltage, like pressure in a fluid, is applied across two points in a
circuit. Voltage does not “flow through a circuit”.
The voltage across a single component depends on three factors: the component itself
(the electrical resistance of the component), the resistance of all the other components
in the circuit, and the total voltage of the power source.
When you measure the voltage across a light bulb (a device with resistance) the voltage
is high. When you measure the voltage across a length of wire (very low resistance), the
voltage is very low. Ohm’s Law relates current, voltage and resistance.
Current
Current is the flow of electric charge from one point to another within a circuit.
Current depends on the electric potential of the power source and the challenge the
circuit presents to the flow of current known as electrical resistance. The current is the
same at any point in a series circuit. The current is not the same everywhere in a
parallel circuit; it divides between the parallel paths.
Current is a conserved quantity. Thus, in a parallel circuit the total current at the
source (the positive pole of the battery) is equal to the sum of the current flowing in all
the parallel branches:
I total  I1  I 2  I 3 
This of course must also be the total current returned to the negative pole of the
battery.
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