Energy | OCR GCSE Combined Science Physics, Higher tier (J250)

Energy

101 questions
6 subtopics
Paper 12 (Physics)
Paper 12 (Physics)

Energy is examined in Paper 12 (Physics).

It covers conservation of energy, and energy stores, energy changes on heating, and calculating them, energy of a moving body, a spring and a raised object, dissipation, and energy transfer in domestic devices, power ratings, efficiency, and increasing it and reducing unwanted energy transfer, and the rate of cooling.

Sample questions from Energy

Answer each one closed book first, then open the answer.

Conservation of energy, and energy stores

A toy car is given a push along a bench and eventually stops. Account for its energy as a closed system.

Show the answer
The energy in its kinetic store has been transferred to the thermal stores of the car, the bench and the air, so the total is unchanged.
Conservation of energy, and energy stores

A constant force pushes a trolley along a smooth level track. Describe the change in the way energy is stored.

Show the answer
The force does work on the trolley, filling its kinetic store as it speeds up.
Energy changes on heating, and calculating them

A heavy box is dragged at a steady speed across a rough floor. Describe the energy change taking place.

Show the answer
Work is done against friction, transferring energy to the thermal stores of the box, the floor and the surrounding air.
Energy changes on heating, and calculating them

A heater draws a current of 5 A from a 230 V supply for 60 s. How much energy is transferred?

Show the answer
69000 J.
Energy of a moving body, a spring and a raised object

A trolley of mass 8 kg has 100 J in its kinetic store. What is its speed?

Show the answer
5 m/s.
Energy of a moving body, a spring and a raised object

A 2 kg mass falls 5 m with no air resistance. How much energy is in its kinetic store just before it lands, taking g = 10 N/kg?

Show the answer
100 J.
Dissipation, and energy transfer in domestic devices

Does dissipation of energy break the law of conservation of energy?

Show the answer
No, the total energy is unchanged; the energy has only been transferred to less useful stores.
Dissipation, and energy transfer in domestic devices

Describe the useful and wasted transfers in an electric drill.

Show the answer
Energy is usefully transferred to the kinetic store of the rotating bit, and is wasted as heating of the motor and as sound.

The 6 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Conservation of energy, and energy stores	The law of conservation of energy, what a closed system is, why dissipated energy is not lost, and the store changes for thrown stones, braking cars, kettles and freewheeling cyclists.	16
Energy changes on heating, and calculating them	What heating does to the thermal store of a system, specific heat capacity and why water warms slowly, work done by a force against friction and in a heater filament, and calculations of work done, energy transferred electrically, energy to change temperature, and kilowatt-hours and their cost.	16
Energy of a moving body, a spring and a raised object	The equations for the kinetic, gravitational potential and elastic potential stores, with calculations for moving cars and balls, lifted crates, falling masses and stretched springs.	12
Dissipation, and energy transfer in domestic devices	What dissipation means and why dissipated energy is hard to use again, examples from gearboxes, cables, loudspeakers, phones and braking bicycles, and the useful and wasted transfers in torches, drills, fans, heaters and hairdryers powered by batteries or the mains.	16
Power ratings, efficiency, and increasing it	Power as energy transferred each second, what a power rating means, calculations of energy, power and time, why a low-power appliance left on can cost more, calculating efficiency from energies or powers, how lubrication, streamlining, bearings, insulation and thicker cables increase efficiency, and why no device is completely efficient.	23
Reducing unwanted energy transfer, and the rate of cooling	How wall thickness and thermal conductivity decide how fast a building cools, cavity wall and loft insulation, double glazing and draught excluders, how lubricating a bicycle chain or noisy bearings cuts wasted energy, and the surface area of a hot water tank.	18

Energy is 101 of the 1,222 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.