GCSE Physics revision

Energy changes in systems

Energy changes in a system, and the ways energy is stored

AQA 4.1.1.3

Your specification

AQA student objectives

Learning pathway

ALL 🎯

Use ΔE = mcΔθ to calculate thermal energy changes; specific heat capacity is the energy needed to raise 1 kg of a substance by 1°C.

MOST 🎯🎯

Apply the specified scientific knowledge of energy changes in systems to a relevant example.

SOME 🎯🎯🎯

Analyse an unfamiliar example of energy changes in systems using the specified scientific ideas.

Revision summary

Read on screen, then print for Cornell-style active revision.

Energy can be transferred usefully, stored, or dissipated, but it can never be created or destroyed.
Energy can only move between different objects and different forms, meaning the total amount of energy in the universe remains constant.

When charging a phone, electrical energy from the mains supply is transferred to the chemical energy store in the battery.
When using a phone, chemical energy converts back to electrical energy, which powers components such as the screen and speaker.
The screen converts electrical energy into light energy, whilst the speaker converts it into sound energy.

2. Energy Transfers in Everyday DevicesAQA

When charging a phone, electrical energy from the mains supply is transferred to the chemical energy store in the battery.
When using a phone, chemical energy converts back to electrical energy, which powers components such as the screen and speaker.
The screen converts electrical energy into light energy, whilst the speaker converts it into sound energy.

In an ideal energy transfer, all energy would be converted into the desired useful form.
In reality, some energy is dissipated as wasted energy, meaning it is transferred to unintended forms.
Wasted energy is most commonly released as heat, which is why devices like phones warm up during use or charging, though it can also be lost as sound.

3. Useful and Wasted EnergyAQA

In an ideal energy transfer, all energy would be converted into the desired useful form.
In reality, some energy is dissipated as wasted energy, meaning it is transferred to unintended forms.
Wasted energy is most commonly released as heat, which is why devices like phones warm up during use or charging, though it can also be lost as sound.

In physics, a system is a defined portion of the physical universe chosen for analysis.
Everything outside the chosen system is referred to as the environment.

An open system is one in which energy and matter can freely move between the system and the environment.
A phone is an example of an open system, as heat energy can be transferred from the phone to the surroundings, such as the air or your skin.

A closed system is one in which energy and matter cannot enter or escape the system.
In a closed system, any energy dissipated (e.g. heat) remains within the system rather than being lost to the environment.
The overall energy of a closed system never changes, which is a direct consequence of the conservation of energy principle.