Physics - Making use of energy Flashcards
Name the three ways in which heat energy can be transferred when there is a temperature difference
- Conduction
- Convection
- Radiation
Explain thermal conduction
Metals are usually good conductors. Non-metals e.g. plastic and gases are usually poor conductors.
Poor conductors are called insulators.
Heat energy is conducted from the hot end of an object to the cold end, e.g. a metal spoon in a cup of hot water - the end not in the water soon becomes hot too.
Explain thermal convection
Thermal convection occurs in gases and liquids.
As gases and liquids heat up they expand and become less dense.
Because warm gases/liquids are less dense than nearby colder gases/liquids they rise and the colder gases/liquids fall.
Explain thermal radiation
Heat transferred by infrared radiation.
Unlike conduction and convection - which need particles - infrared radiation is a type of electromagnetic radiation that involves waves.
Because no particles are involved, radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun even though it is 150 million kilometres from the Earth.
Look at these two houses.
Describe the difference and explain what may have been done.
The house on the left is losing a lot of heat through the windows and door.
The house on the right isn’t - it has been double glazed
How does double glazing work to conserve energy?
Double glazing has air or a vacuum between two panes of glass.
Conduction and convection are both minimised because the air between the panes of glass is a poor conductor of heat, and convection is reduced because there isn’t much room for the air to move.
How does cavity wall insulation conserve energy?
Insulation is placed inbetween the bricks and the inner wall where the cavity is.
The insulating material contains pockets of trapped air. This reduces conduction and convection.
Sometimes cavity wall insulation has a layer of silver foil in order - this reflects infrared radiation back into the building.
How does loft insulation work?
Loft insulation works in the same way as cavity wall insulation.
It traps air and reduces convection and conduction.
How do you calculate the cost effectiveness and efficiency of different methods of reducing energy loss from the home
Installing double glazing or extra insulation to reduce heat energy losses eventually saves money but to start with it costs money to buy and install.
The payback time is the time it takes to save as much money from energy saving as it cost to buy and install the insultation.
