AQA GCSE Physics
AQA GCSE Physics 4.2.4 Energy Transfers Exam Questions
Free AQA GCSE Physics exam questions for 4.2.4 Energy Transfers, with a mark scheme for every pack. Covers electrical power equations, energy transferred by appliances, E = Pt and E = QV, and transformers in the national grid.
4.2.4 Energy Transfers exam questions
3 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Physics 4.2.4 Energy Transfers
In AQA GCSE Physics, 4.2.4 links electricity back to energy. It covers power in circuits, the energy transferred by everyday appliances and how the national grid distributes electricity efficiently using step-up and step-down transformers. It is examined on Paper 1. The power and energy equations here are among the most used in the electricity topic, and examiners regularly set multi-step calculations as well as explanations of why the grid transmits electricity at high potential difference.
What you need to know
- Power in circuits P = V I and P = I^2 R, where P is power in W, V is p.d. in V, I is current in A and R is resistance in Ω. Both must be memorised.
- Energy transferred by appliances Everyday appliances transfer energy from batteries or the mains to the kinetic energy of motors or the thermal energy of heating devices. The amount depends on the power of the appliance and how long it is switched on for.
- Energy equations E = P t and E = Q V, where E is energy in J, t is time in s and Q is charge in C. Work is done when charge flows in a circuit.
- Power ratings The power rating of an appliance tells you the energy transferred per second when it is in use, for example a 2 kW kettle transfers 2000 J each second.
- The national grid The national grid is a system of cables and transformers linking power stations to consumers. Step-up transformers increase the p.d. from the power station to the transmission cables; step-down transformers decrease it to a safer level for homes.
- Why high p.d. is used For a given power, a high transmission p.d. means a lower current. A lower current means less energy is dissipated by heating in the cables, so the grid is an efficient way to transfer energy.
- Transformer equation For a 100% efficient transformer, V_p x I_p = V_s x I_s (on the equation sheet). Power in equals power out.
Common mistakes in 4.2.4 Energy Transfers
- Saying high p.d. reduces resistance in the cables. Resistance does not change; the lower current reduces heating (P = I^2 R).
- Mixing up step-up and step-down transformers. Step-up is at the power station end; step-down is near homes.
- Using time in minutes or hours with E = P t. Convert to seconds when using watts.
- Forgetting to square the current in P = I^2 R.
Try three 4.2.4 Energy Transfers exam-style questions
1. A 2.0 kW kettle is switched on for 3 minutes. Calculate the energy transferred. (3 marks)
Show the mark scheme answer
P = 2000 W, t = 180 s; E = P t = 2000 x 180; = 360 000 J.
2. A heater has a resistance of 20 Ω and a current of 5.0 A through it. Calculate its power. (2 marks)
Show the mark scheme answer
P = I^2 R = 5.0^2 x 20; = 500 W.
3. Explain why electricity is transmitted through the national grid at a very high potential difference. (3 marks)
Show the mark scheme answer
Step-up transformers increase the p.d. so the current is lower for the same power; a lower current means less energy is dissipated by heating in the cables (P = I^2 R); so transmission is more efficient.
4.2.4 Energy Transfers FAQs
What does AQA GCSE Physics 4.2.4 Energy transfers cover?
It covers electrical power, energy transferred by appliances using E = P t and E = Q V, and how the national grid uses transformers to transmit electricity efficiently.
Which power equations do I need for electricity?
Learn P = V I, P = I^2 R, E = P t and E = Q V. The transformer equation V_p I_p = V_s I_s is on the equation sheet.
What is the key point to remember about the national grid?
High potential difference means low current, and low current means less energy is wasted heating the cables. Always link the lower current to reduced heating.
