✓ Revise Right course
The formula for electrical power is P = VI: power in watts equals potential difference in volts times current in amperes. Free GCSE Physics notes.
Understanding Electrical Power is part of Energy transfers in GCSE AQA Higher Physics.
4 min
Reading time
24
Lessons in this topic
GCSE AQA Higher
Pathway
Reviewed by Revise Right
Content review
The formula for electrical power is P = VI: power in watts equals potential difference in volts times current in amperes. Free GCSE Physics notes.
AQA GCSE Physics mock draft, 26–31 Oct. Draft coverage: Physics Paper 1 (Higher tier). Reviewed for an original-practice sitting; check student availability before registering. Marking and results will follow later, after separate approval. Eligible new accounts receive a five-day Pro trial when signup email verification completes. Previous trials keep their original expiry. After expiry, new papers need Pro unless you have an explicitly confirmed free sitting offer for this event. That offer adds no Pro time or AI learning. Saved attempts and released results remain readable. No card or automatic charge.
Use this lesson to stay inside Energy transfers while connecting the detail back to the wider Electricity topic.
Read the core explanations from Understanding Electrical Power before testing yourself from memory.
Your phone charger gets warm when plugging in. Your kettle uses more electricity than your LED bulb. Why do some electrical devices transfer energy faster than others?
The answer lies in electrical power - the rate at which electrical energy gets transferred. Understanding power helps you work out electricity bills, choose efficient appliances, and solve circuit problems in exams.
Power connects three key electrical quantities: energy, voltage, and current. Once you see how they link together, circuit calculations become much clearer.
Think of power as 'energy per second'. A 100W bulb transfers 100 joules of electrical energy every second. A 2000W kettle transfers energy twenty times faster - that's why it heats water so quickly.
Voltage is like electrical pressure. Higher voltage pushes charge carriers with more energy. A 12V car battery gives each coulomb of charge 12 joules of energy to transfer around the circuit.
Current tells you how much charge flows past a point each second. One ampere means one coulomb of charge flowing per second. More current means more charge carriers available to transfer energy.
Power depends on two factors: how much energy each charge carrier has (voltage) and how many charge carriers flow per second (current). This gives us the fundamental power equation.
This formula makes intuitive sense. Double the voltage and you double the energy each charge carrier has. Double the current and you double the number of charge carriers flowing. Either way, you double the power.
The units work out perfectly too. Volts are joules per coulomb (J/C) and amperes are coulombs per second (C/s). Multiply them together: (J/C) × (C/s) = J/s = watts.
You can rearrange this formula to find any quantity if you know the other two. Need current? Use I = P/V. Need voltage? Use V = P/I. The triangle method works well for remembering these rearrangements.
Let's apply the power formula to some typical exam questions. These calculations appear frequently in GCSE papers, so getting the method right is crucial for full marks.
Worked example: Calculating Power from Voltage and Current
A hairdryer operates at 230V and draws a current of 8.7A. Calculate its power rating. [3 marks]
Answer: 2001 W (or 2.0 kW to 2 significant figures)
Notice how we kept all the working clear and included units at each step. Examiners award method marks for the correct formula and substitution, even if your final calculation is wrong.
Worked example: Finding Current from Power and Voltage
A 60W light bulb operates at 12V. Calculate the current through the bulb. [3 marks]
Answer: 5 A
Power and energy are closely related but different quantities. Power is the rate of energy transfer - how quickly energy gets converted from one form to another.
Energy is the total amount transferred over time. If you know the power and the time, you can calculate energy using: Energy = Power × Time. This is why electricity bills measure energy in kilowatt-hours (kWh).
A 2kW kettle running for 0.1 hours (6 minutes) uses 2 × 0.1 = 0.2 kWh of energy. At 15p per kWh, this costs 3p. Understanding this connection helps you work out running costs for electrical appliances.
In circuits, power tells you how quickly components convert electrical energy into other forms. Resistors convert electrical energy to heat. Motors convert it to kinetic energy. LEDs convert it to light energy.
Power calculations are straightforward if you follow the method systematically. However, students often lose marks through careless errors rather than not knowing the physics.
Always start by writing down the formula, even for simple calculations. This shows the examiner your method and earns you a method mark. Then substitute the values clearly, showing which number corresponds to which variable.
Watch out for unit conversions. Power might be given in kilowatts (kW) when you need watts (W). Remember: 1 kW = 1000 W. Current might be in milliamps (mA) when you need amps (A). Remember: 1000 mA = 1 A.
Check your final answer makes sense. A typical household appliance has power between 10W (LED bulb) and 3000W (kettle). If you calculate 50,000W for a toaster, you've probably made an error.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The formula for electrical power is P = VI: power in watts equals potential difference in volts times current in amperes. It rearranges to I = P/V to find current and V = P/I to find voltage.
Power is calculated by multiplying voltage and current with P = VI. A hairdryer operating at 230V and drawing a current of 8.7A has a power rating of 230 × 8.7 = 2001 W, or 2.0 kW to 2 significant figures.
Current is found by rearranging P = VI to I = P/V. A 60W light bulb operating at 12V has a current of 60 ÷ 12 = 5 A flowing through it.
Electrical power is the rate of energy transfer in an electrical circuit, measured in watts (W). It is energy per second, so a 100 W bulb transfers 100 joules of electrical energy every second.
Volts times amps gives watts because volts are joules per coulomb (J/C) and amperes are coulombs per second (C/s). Multiplying them gives (J/C) × (C/s) = J/s, which is watts, the rate of energy transfer.
Running cost is found from the energy used in kilowatt-hours (power in kW × time in hours) × the price per kWh. A 2kW kettle running for 0.1 hours (6 minutes) uses 2 × 0.1 = 0.2 kWh, which at 15p per kWh costs 3p.
A hairdryer at 230 V drawing 8.7 A has a power rating of 2001 W, or 2.0 kW to 2 significant figures. Using P = VI, P = 230 × 8.7 = 2001 W.
A 60 W light bulb operating at 12 V has a current of 5 A through it. Rearranging P = VI gives I = P ÷ V = 60 ÷ 12 = 5 A.
Voltage is found from power and current by rearranging P = VI to V = P/I. The triangle method helps to remember the rearrangements, including I = P/V for current.
A 12 V battery gives each coulomb of charge 12 joules of energy to transfer around the circuit. Potential difference, or voltage, is the energy transferred per unit charge between two points, measured in volts.
A typical household appliance has a power between 10 W, for an LED bulb, and 3000 W, for a kettle. A calculated power of 50,000 W for a toaster would probably mean an error.
Doubling the voltage doubles the power, because P = VI and each charge carrier has double the energy. Doubling the current also doubles the power, because twice as many charge carriers flow each second.
A kettle heats water quickly because its power is high: a 2000 W kettle transfers energy twenty times faster than a 100 W bulb. Power is the rate at which electrical energy gets transferred.
Power calculations often need kilowatts converted to watts, where 1 kW = 1000 W, and milliamps converted to amps, where 1000 mA = 1 A. Writing down the formula first and substituting values clearly earns method marks.
Different components convert electrical energy into different forms: resistors convert it to heat, motors to kinetic energy and LEDs to light energy. Power gives how quickly each component converts the energy.