# 2.1.3 Current, Resistance & Potential Difference

### Current, Resistance & Potential Difference

• Resistance is defined as the opposition to current:
• The higher the resistance of a circuit, the lower the current
• This means that good conductors have a low resistance and insulators have a high resistance
• The symbol for resistance is R
• It is measured in Ohms (Ω)
• Ω is the Greek capital letter ‘Omega’
• An Ohm is defined as one volt per ampere (1 V / A)
• The resistance of a circuit can be increased by adding resistors (or variable resistors) to it
• Every electrical component has a resistance, even wires
• In exam questions, the resistance of the wires and batteries are assumed to be negligible High resistance means there is lower current and vice versa

• The current I through a component depends on both the resistance R of the component and the potential difference V across the component
• The greater the resistance R of the component, the lower the current I for a given potential difference V across the component
• The lower the resistance R of the component, the greater the current I for a given potential difference V across the component

### Calculating Current, Resistance & Potential Difference

• The current, resistance and potential difference of a component in a circuit are calculated using the equation: • This equation can be rearranged with the help of the following formula triangle: Voltage, current, resistance formula triangle

#### Worked Example

Calculate the potential difference through a resistor of resistance 10 Ω if there is a current of 0.3 A through it.

Step 1: List the known quantities

• Resistance, R = 10 Ω
• Current, I = 0.3 A

Step 2: Write the equation relating resistance, potential difference and current

V = IR

Step 3: Substitute in the values

V = 0.3 × 10 = 3 V

#### Exam Tip

Remember that ‘voltage’ and ‘potential difference’ are the same, either wording will be accepted in your exam answers ### 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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