Physics AQA Topic 1 (Conservation and dissipation of energy)

4.1.2

What is a system

An object or group of objects

What are open systems

They are able to exchange energy and matter with their surroundings

What are closed systems

They are unable to exchange energy and matter with their surroundings

State the law of energy consumption

Energy cannot be created or destroyed (it can be transferred into different forms, stored, and dissipated)

Is there a change in energy when there are energy transfers made in a closed system

No - there is no net change to the total energy

State any changes in the total energy of a ball that is kicked (assuming that no external forces act so it is a closed system)

The total energy of the system remains constant due to the conservation of energy

What happens to the rate of energy transfer when the thermal conductivity of a material is high

The rate of energy transfer by conduction across the material is higher

What is the rate of cooling of a building affected by

It is affected by the thickness and thermal conductivity of its walls

Do double-glazed windows have a higher or lower thermal conductivity then single-glazed windows

Lower - meaning less energy transfers through them

Describe three methods of reducing heat loss in a building

Double glazing, loft and wall insulation, and having thicker walls

State two equations to calculate efficiency

Efficiency = useful output energy transfer/total input energy transfer, efficiency = useful power output/total power output

How can the efficiency of a system be increased

Reducing and recycling the waste energy transfer output

What is waste energy

Energy that is transferred into useless stores - it is not used for its desired purpose

Describe the energy changes that occur in a filament light bulb

Electrical energy is transferred into light and heat energy - light is the useful energy form, heat is the waste energy

What are some ways of reducing unwanted energy transfers

Through lubrication and the use of thermal insulation

How can the efficiency of a mechanical machine with moving parts be improved

Lubricate any moving parts to reduce the friction and energy loss due to heating

How can the efficiency of a radiator be improved

Installing metal foil sheets behind the radiator to reflect the heat back into the room rather than the heat being absorbed into the walls

How can the efficiency of boiling water in a pan be improved

By placing a lid on the pan to reduce the heat loss from the top