Resistance (Edexcel IGCSE Physics: Double Science)
Revision Note
Author
AshikaExpertise
Physics Project Lead
Calculating 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 a 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
- 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 voltage across 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
You've read 0 of your 0 free revision notes
Get unlimited access
to absolutely everything:
- Downloadable PDFs
- Unlimited Revision Notes
- Topic Questions
- Past Papers
- Model Answers
- Videos (Maths and Science)
Did this page help you?