WALT: about resistance and Ohm‘s law Success Criteria: You should know and understand the relationship between voltage, current and resistance.

Why do we get resistance? An electric current flows when charged particles called electrons move through a conductor. All the parts of a circuit will try to stop the electrons going through them. This is called resistance. The resistance of a material depends on; – Length – Type of material – Thickness – Temperature Resistance in a wire increases as: – the length of the wire increases – the thickness of the wire decreases – the temperature increases Resistance (R) ohms

Model of Resistance – Imagine a three-lane road and a single-lane road with cars all going at the same speed. More cars pass per second in the wider road even though the speed is the same. More cars (charges) per second means higher current for a given voltage and so smaller resistance.

Resistance and Temperature The resistance of a wire also depends on is temperature. A hot wire has a higher resistance than a cold wire because electrons get bashed about more by the atoms.

Electrical Symbols

What is a resistor Resistors are designed to slow down the current and reduce the voltage.

A Variable Resistor A variable resistor is used to control the size of a current by altering the resitance. Moving the slider controls the length of the wire the current has to pass through.

Ohm‘s Law Ohm's Law was derived experimentally by the German physicist Georg Simon Ohm in Ohm's Law states that in an electrical conductor the ratio of potential difference (voltage) to current is constant.

Example What is the value of this resistor, in ohms (Ω)? Resistor value = 2700 Ω, or 2.7 kΩ.