Loading…
Loading…
Loading…
OCR GCSE Physics A · J249
OCR J249 · P7.1c Check the specification (PDF) (opens in a new tab)
A system is the object or group of objects you choose to study. When it changes, energy may move between its stores or cross its boundary. Heating, a force causing movement, and an are three ways energy can be transferred. Energy is not used up: if one store decreases, another store increases, perhaps in the surroundings.
Imagine a metal block warmed by a heater. Energy is transferred to the block by heating, increasing its internal energy—the energy associated with the motion and positions of its particles. If the block remains solid, its temperature rises. Temperature indicates how hot the block is; it is not the same as the total energy stored in it.
How much its temperature rises depends on the block’s mass and material as well as the energy transferred. A larger mass of the same material needs more energy for the same temperature rise. Materials also differ in specific heat capacity: this tells us how much energy is needed to raise the temperature of 1 kg by 1 °C. A material with a higher specific heat capacity needs more energy for that rise, so equal masses given equal amounts of energy would generally show a smaller temperature rise. Specific heat capacity is measured in joules per kilogram per degree Celsius, J/(kg °C). If a substance is changing state, its internal energy can increase without a temperature rise; the temperature-rise description applies when its state does not change.
When a force acts and an object moves in the force’s direction, the force does work: it transfers energy. Push a stationary trolley and energy is transferred to its kinetic store as it speeds up. Lift it and energy is transferred to its gravitational potential store. Friction can also do work, transferring energy from a moving object’s kinetic store to the internal energy stores of the object and its surroundings. The force is involved in the transfer; force itself is not an energy store.
An electric current is a flow of charge. When current flows through a component, energy is transferred electrically to it: this is electrical work done. In a battery-powered lamp, the battery’s chemical energy store decreases while energy is transferred to the lamp. The lamp’s internal energy increases as it warms, and light carries energy to the surroundings.
An electric kettle shows two pathways in sequence. Current transfers energy electrically to its heating element; the hot element then transfers energy by heating to the water, increasing the water’s internal energy and temperature. Identifying each step makes clear how the water is heated without treating electricity or heat as substances stored in the kettle.
Across a complete account, energy is conserved: a decrease in one store is matched by increases elsewhere.
Name both the energy store that decreases and the store that increases; saying that energy is ‘used up’ does not describe a transfer.
Do not confuse temperature with energy: equal masses of different materials can have different temperature rises after receiving the same energy.
For a force, describe what moves while the force acts. For a circuit, identify the component receiving energy while current flows.
It can see this note and what your specification asks for.
Answers are free with an account.
1 free note left this week
Get more free notesYour answer sets when this note comes back for review, or marks it complete.
Was this note helpful?
Log in to tell us whether it helped, or to report a problem.
Last updated
System
An object or group of objects chosen for studying energy transfers and changes in energy stores.
Internal energy
The total kinetic and potential energy of the particles in a substance.
Specific heat capacity
The energy needed to raise the temperature of 1 kg of a material by 1 °C, without changing its state.
Work done by a force
Energy transferred when a force causes an object to move through a distance.
Electric current
The flow of electric charge.
Electrical work done
Energy transferred to a component when charge flows through it.
Put your knowledge into practice — try past paper questions for Physics A
System
An object or group of objects chosen for studying energy transfers and changes in energy stores.
Internal energy
The total kinetic and potential energy of the particles in a substance.
Specific heat capacity
The energy needed to raise the temperature of 1 kg of a material by 1 °C, without changing its state.
Work done by a force
Energy transferred when a force causes an object to move through a distance.
Electric current
The flow of electric charge.
Electrical work done
Energy transferred to a component when charge flows through it.