RESISTANCE

==Resistance== Resistance is a measure of how much a component resists the flow of current. Resistance is measured in '''ohms (Ω)'''. The greater the resistance of a component the less current it allows to flow through the circuit. Resistors can be thought of as current controllers (just like a floodgate controls how much water can flow). The electrons require a force and energy (a voltage) to move through a resistor and therefore will lose energy as they pass through it (voltage drop). Symbols for common resistors: [image:http://i.imgur.com/6Qr9tE8.gif] Some resistors are variable. This means that they can be used to control the amount of current flowing through the circuit. The '''Rheostat or Variable Resistor''' above is a good example; sliding the controller one way increases the resistance and therefore reduces the current. Likewise sliding it the other way reduces the resistance, increasing the current that can flow through. Variable resistors are often used as dimmer switches and volume controls, etc. ==Resistance Calculations== Resistance is defined as the ratio of Voltage across a component to the Current going through it. The formula for Resistance is: $$R=\frac{V}{I}$$ ==Examples== '''E.G.''' A 5.0Ω resistor is placed in series with an ammeter which reads 1.2A. Calculate the voltage across the resistor. $$V=IR$$ $$V = 1.2 \times 5.0$$ $$V = 6.0V$$ '''E.G.''' Calculate the current running through this resistor: [image:http://i.imgur.com/NxIolx9.png] $$I=\frac{V}{R}$$ $$I=\frac{5}{10}$$ $$I = 0.5A$$