Circuits and YOU!

One of the most fundamental components is the resistor. The resistor allows one to control the current flow in a circuit. The base unit for a resistor is the ohm which is denoted by a capital omega.

The fundamental formula for a resistor is ohm's law which states V=IR.

The simplest circuit one can construct is a resistor across a voltage source.

A 1Kohm resistor across a source. The resistor is denoted by a squiggly line and the power source is denoted by the parallel lines. In this circuit we have a 1Kohm resistor across a varying DC source, at 10 volts the resistor will have 10miliamps running through it.

Ohm's law is shown by the following graph which shows current vs voltage. The slope is resistance.

(Y axis is in mA while X is in Volts)

This is very simple circuit yet, most complicated circuits can be redrawn as a equivalence circuit involving a single power source and a single resistor.

Resistors can be hooked up two ways, series and parallel.

Series:

Series is a type of circuit where everything is hooked up in a line, the charge that goes through one device goes through all the rest in that line, since charge has to conserved. The voltages across all the devices are not the same as they all add up to the source voltage.

In series, resistance adds up so that:

In this setup the two 1Kohm resistors act like 1 2Kohm resistor.

Other facts in series, the current through resistors in series is all the same, the current into one the device is the same as the other. The voltage is not the same though each device (unless same values). Two Resistors in series is known as a voltage divider.
The Vout is found by the following formula

This states that resistances in series add up, those two 1Kohm resistors form an equivalence 2Kohm resistor.

Parallel

In parallel the circuit branches off into two or more components. In parallel the voltages are the same across two devices, however the current is not.

The following circuit shows two resistors in parallel, their values are 1Kohm and 2Kohm respectively.

They both have the same potential through them, however their resistances draw differing amounts of current. Their equivalence resistance is shown by the following

As you can see the current through each resistor is different, however they add up to the total current through them

Parallel is useful when you want the same potential across many components. In parallel components can draw more power than in series.

The Resistor is a fundamental part of all circuits, it is essential to be able control current and source the correct amount of power to parts in your circuit.

Formula Sheet.
Ohm's Law

Power

Resistor in Series

Resistor in Parallel

Voltage Divider