- Define and explain Electrical Power in your own words
- Use key terms such as voltage accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Electrical Power: calculating power with P = I × V and the energy transferred.
Calculating power with P = I × V and the energy transferred.
Key ideas
Current is moving charge
In metals, current is a flow of electrons. Charge Q = current × time, so 2 A for 3 s moves 6 C of charge. An ammeter measures current and is connected in series; conventional current is drawn as flowing from positive to negative, opposite to the electron flow.
Voltage, current and resistance are linked by V = IR
Voltage drives current through resistance like pressure drives water through a pipe. Doubling the voltage doubles the current through a fixed resistor. Ohmic conductors give a straight-line current–voltage graph through the origin — this is Ohm's law.
Key term — voltage: The energy transferred per unit charge, measured in volts (V) — the 'push' driving the current.
A kettle draws 5 A from the 230 V mains. Calculate its power.
5 × 230 = 1150 W.
Answer: 5 × 230 = 1150 W.
- Saying current is 'used up' in a circuit Current is the same all round a series loop; it is energy that is transferred to the components.
- Connecting a voltmeter in series Voltmeters connect in parallel across the component — in series they would block the current.
Practice
100 × 60 = 6000 J.
0.5 × 20 = 10 C.
12 ÷ 2 = 6 Ω.
Total R = 12 Ω, so I = 12 ÷ 12 = 1 A.
Quick check
Which of these best defines "voltage"?
Why does one blown bulb not darken the other bulbs in a house?
- Electrical Power: calculating power with P = I × V and the energy transferred.
- Current is moving charge: In metals, current is a flow of electrons.
- power: The rate of energy transfer, measured in watts (W).
- Watch out for: saying current is 'used up' in a circuit