Physics · StudentHub Lesson
Electric circuits
Current, voltage and resistance in series and parallel circuits.
What you will learn
- Define current, voltage and resistance
- Use V = I × R
- Compare series and parallel circuits
- Read simple circuit diagrams
- Explain why houses use parallel wiring
Watch the lesson
We haven’t confirmed a lesson video that matches this topic closely enough yet, so the notes below are the lesson for now. A recommended video will be added once we’ve checked one properly.
Topic notes
Main Idea
An electric circuit is a closed loop that lets charge flow. Voltage pushes the charge, current is the rate of flow, and resistance opposes it.
Key Concepts
- Current is measured in amps (A) with an ammeter in series
- Voltage is measured in volts (V) with a voltmeter in parallel
- Ohm's law: V = I × R
- In series, current is the same everywhere and voltages add
- In parallel, voltage is the same across each branch and currents add
Definitions
- Current: The rate of flow of electric charge, measured in amps.
- Voltage: The energy pushing charge around a circuit, measured in volts.
- Resistance: How much a component opposes current, measured in ohms (Ω).
Worked Example
A 12 V battery is connected to a 4 Ω resistor. What current flows?
- Use V = I × R
- Rearrange: I = V ÷ R
- I = 12 ÷ 4
Answer: 3 A
Common Mistakes
- Thinking current is 'used up' by bulbs
- Connecting a voltmeter in series
- Assuming adding resistors in parallel increases total resistance
Key concepts
Important terms
- Current
- The rate of flow of electric charge, measured in amps.
- Voltage
- The energy pushing charge around a circuit, measured in volts.
- Resistance
- How much a component opposes current, measured in ohms (Ω).
Worked examples
Problem
A 12 V battery is connected to a 4 Ω resistor. What current flows?
- 1. Use V = I × R
- 2. Rearrange: I = V ÷ R
- 3. I = 12 ÷ 4
Answer: 3 A
Quick revision
- V = I × R
- Ammeter in series, voltmeter in parallel
- Series: same current, voltages add
- Parallel: same voltage, currents add
- Homes use parallel so devices work independently
Check your understanding
Question 1 · Multiple choice
What is the unit of resistance?
Question 2 · Short answer
Current is 2 A through a 5 Ω resistor. What is the voltage?
Question 3 · True or false
In a series circuit, if one bulb breaks the others stay lit.
Done with Electric circuits?
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