Topic 1: Energy Flashcards
What is a system?
An object or group of objects
What are the 8 energy stores?
- Thermal
- Kinetic
- GPE
- EP
- Chemical
- Magnetic
- Electrostatic
- Nuclear
How can energy be transferred? [4]
- Mechanically
- Electrically
- Heating
- Radiation
What is a closed system?
A system where neither matter nor energy can enter or leave
Describe the energy changes when boiling water in a kettle [2]
- Energy is transferred electrically to the thermal energy store of the kettle’s heating element
- This transfers energy by heating to the water’s thermal energy store
In which 2 ways can work be done?
- When current flows
- A force moving an object
Describe the energy changes when an object is projected upwards [2]
- The initial force exerted by a person to throw an object upwards does work
- It causes an energy transfer from the chemical energy store of the person’s arm to the kinetic energy store of the object and arm
Describe the energy changes when a ball is dropped [2]
- The gravitational force causing the ball to drop does work
- It causes energy to be transferred from the ball’s GPE store to its kinetic energy store
Describe the energy transfers when a car brakes [2]
- The friction between a car’s brakes and its wheels does work
- It causes an energy transfer from the wheel’s kinetic energy stores to the thermal energy store of the surroundings
Describe the energy changes when a car collides [2]
- The normal contact force between a car and the object does work
- It causes energy to be transferred from the car’s kinetic energy store to other energy stores
What is specific heat capacity?
The amount of energy required to raise the temperature of 1kg of the substance by 1°C
What is power?
The rate at which energy is transferred or the rate at which work is done
An energy transfer of 1 joule per second is equal to how many watts?
1 watt of power
State the conservation of energy principle
Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed
Explain how energy in a phone is:
i) used usefully
ii) dissipated/wasted
- Energy is transferred usefully from the chemical energy store of the battery in the phone
- Some of this energy is dissipated to the thermal energy store of the phone
Explain how energy when a cold spoon is dropped in hot food is:
i) transferred
ii) not dissipated/wasted
- Energy is transferred from the thermal energy store of the soup to the thermal energy store of the spoon
- No energy has left the closed system, so the net change in energy is 0
Explain how lubrication reduces unwanted energy changes [4]
- Whenever something moves, there’s usually at least one frictional force acting against it
- This causes some energy in the sytem to be dissipated
- Using lubricants can be used to reduce the frictional force of objects when they move
- This reduces the amount of energy dissipated/wasted
How can the rate of cooling of a building be reduced? [2]
- Thick walls
- Made from a material with a low thermal conductivity
How do cavity walls reduce energy transfers? [2]
- They contain air gaps
- These air gaps reduce the amount of energy transferred by conduction through the walls
How do cavity walls (with foam) reduce energy transfers? [2]
- Air gap is filled with foam
- Reduces energy transfer by convection
How does loft insulation reduce energy transfers?
Reduces energy transfers by convection
How do double-glazed windows reduce energy transfers? [2]
- Air gap between two sheets of glass
- Reduces energy transfer by conduction
How do draught excluders reduce energy transfers?
Reduces energy transfers by convection
If a material has a high thermal conductivity, what does that mean?
There is a high rate of energy transfer by conduction across the material
