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Energy changes in a system, and the ways energy is stored before and after such changes
Energy changes in a system is the calculation-heavy foundation of the Energy unit. Students choose a system, identify stores before and after a change, and decide whether the transfer is caused by heating, a force, electric current, or motion. The topic also builds careful unit handling: joules for energy, kilograms for mass, metres for distance, seconds for time, and appropriate constants or quantities. Good revision should focus on choosing the correct relationship before substituting numbers.
43
Objectives
215
Flashcards
215
Questions
90 min
Study time
AQAGCSEPhysicsEnergy
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Syllabus checklist
What you need to know
43 objective pages available
Energy stores and systems12 objectives
- Define a system as an object or a group of objects being considered together.
- Describe how the way energy is stored changes when a physical system changes.
- Describe energy-store changes when an object is projected upwards.
- Describe energy-store changes when a moving object hits an obstacle.
- Describe energy-store changes when an object is accelerated by a constant force.
- Describe energy-store changes when a vehicle slows down.
- Describe energy-store changes when water is heated to boiling in an electric kettle.
- Calculate changes in energy when a system is changed by heating.
- Calculate changes in energy when a system is changed by work done by forces.
- Calculate changes in energy when a system is changed by work done as current flows.
- Use calculations to compare how energy is redistributed in a system on a common scale.
- Link electrical work done and current flow to energy transfers in circuits.
Changes in energy12 objectives
- Calculate the kinetic energy of a moving object using mass and speed.
- Recall and apply the equation Ek = 0.5 x m x v^2.
- Identify kinetic energy in joules, mass in kilograms and speed in metres per second.
- Calculate elastic potential energy stored in a stretched spring within its limit of proportionality.
- Recall and apply the equation Ee = 0.5 x k x e^2.
- Identify elastic potential energy in joules, spring constant in newtons per metre and extension in metres.
- Calculate gravitational potential energy gained by an object raised above ground level.
- Apply the equation Ep = m x g x h when gravitational field strength is given.
- Identify gravitational potential energy in joules, mass in kilograms, gravitational field strength in newtons per kilogram and height in metres.
- Rearrange energy equations to find mass, speed, spring constant, extension, gravitational field strength or height where appropriate.
- Required practical: investigate the transfer of energy from a gravitational potential energy store to a kinetic energy store.
- Interpret experimental data from energy-transfer investigations.
Energy changes in systems10 objectives
- Calculate the change in thermal energy when the temperature of a system changes.
- Apply the equation change in thermal energy = mass x specific heat capacity x temperature change.
- Identify change in thermal energy in joules, mass in kilograms, specific heat capacity in joules per kilogram per degree Celsius and temperature change in degrees Celsius.
- Define specific heat capacity as the energy needed to raise the temperature of one kilogram of a substance by one degree Celsius.
- Explain how energy supplied to a material links to its mass, temperature change and specific heat capacity.
- Rearrange the specific heat capacity equation to calculate mass, specific heat capacity or temperature change.
- Required practical activity 1: determine the specific heat capacity of one or more materials.
- Link the decrease of one energy store or work done to the increase in thermal energy stored by a material.
- Interpret data from a specific heat capacity investigation, including temperature change and energy supplied.
- Identify apparatus and techniques used in specific heat capacity practical work.
Power9 objectives
- Define power as the rate at which energy is transferred.
- Define power as the rate at which work is done.
- Calculate power using energy transferred divided by time.
- Calculate power using work done divided by time.
- Recall that 1 watt is equivalent to 1 joule per second.
- Identify power in watts, energy transferred in joules, work done in joules and time in seconds.
- Compare devices with different power ratings using energy-transfer examples.
- Explain why two devices can transfer the same amount of energy but have different powers if one transfers it faster.
- Rearrange power equations to calculate energy transferred, work done or time.
Key terms
systemenergy storeenergy storagephysical systemenergy-storeprojected objectobstacleconstant forcekinetic energyboiling pointheatingwork done
Exam tips
- Understand the Concept of a System: When defining a system, clearly identify the object or group of objects being considered together. Use diagrams if necessary to visualize the system boundaries.
- Understand Energy Storage Changes: When studying energy changes in systems, focus on how energy is stored before and after a physical change. Use diagrams to visualize these changes.
Common mistakes
- Misunderstanding System Definition: Emphasize that a system can include multiple objects interacting with each other, not just one.
- Misunderstanding Energy Storage Changes: Emphasize that energy storage can change, such as when potential energy converts to kinetic energy during motion.
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