# 11.2.1 Resistance

### Defining Resistance

• Resistance is defined as the opposition to current
• For a given potential difference: The higher the resistance the lower the current
• Wires are often made from copper because copper has a low electrical resistance. This is also known as a good conductor
• The resistance R of a conductor is defined as the ratio of the potential difference V across to the current I in it

Resistance of a component is the ratio of the potential difference and current

• Resistance is measured in Ohms (Ω)
• An Ohm is defined as one volt per ampere
• The resistance controls the size of the current in a circuit
• A higher resistance means a smaller current
• A lower resistance means a larger current
• All electrical components, including wires, have some value of resistance

### Calculating Resistance

#### Determining Resistance

• To find the resistance of a component, we can set up a circuit like the one shown below

A circuit to determine the resistance of a component

• The power supply should be set to a low voltage to avoid heating the component, typically 1-2 V
• Measurements of the potential difference and current should then be taken from the voltmeter and ammeter respectively
• Finally, these readings should be substituted into the resistance equation

#### Worked Example

A charge of 5.0 C passes through a resistor of resistance R Ω at a constant rate in 30 s.

If the potential difference across the resistor is 2.0 V, calculate the value of R.

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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