P1.1 Flashcards
What type of radiation doesn’t require particles?
Infrared
What can infrared radiation be detected with?
A thermogram
What objects are best at absorbing and emitting?
Dull, Matt objects
Why are metals good conductors of heat?
The atoms are arranged in neat rows and columns and they have delocalised electrons that can move freely
Why are plastic, wood and polystyrene bad conductors of heat?
Their atoms are not arranged neatly and there are no delocalised electrons
What does convection happen in?
Liquids and gases
What do insulators do?
Keep warmth from leaving and entering
Describe the process of convection
The particles are heated and gain energy, then they separate and become less dense and rise. When they rise they get further away from the heat so cool down, lose energy, become more dense and fall back down again
Why do solids, liquids and gases expand when they’re heated?
The particles gain more energy and vibrate more, causing them to take up more space
What is the kinetic theory?
Particles in solids, liquids and gases have different amounts of energy
What can you do to increase heat transfer?
Increase surface area
Change surface that object is on
Use a metal surface as its a good conductor
Cooling fins are used at the back of fridges, car radiators etc. Why do they have such a large surface area?
To stop them getting hot
What adaptations do animals living in hot climates have?
Large ears as they have a large surface area and keeps them cool
How are animals adapted to live in cold climates?
Having a large volume and small surface area
Small ears
What does U-Values measure?
The rate of heat transfer through a material
What does high U-Value mean?
Lots of heat energy is transferred
What does low U-Value mean?
Little heat energy is transferred (ideal for houses)
What is specific heat capacity?
The amount of energy required to raise 1kg of a substance by 1 degrees Celsius
How does liquid evaporate?
The top layer of particles absorb heat energy from the surroundings which causes them to vibrate more. This allows them to break the forces of attraction and escape with their heat as gas particles. This gradual change of state makes the liquid cool down as small amounts of heat escape
What are the properties of a solid?
Low particle energy
Fixed volume
Fixed shape
What are the properties of a liquid?
Medium particle energy
Fixed volume
Takes the shape of its container
What are the properties of a gas?
High particle energy
Far apart
Fill the available space
What’s the definition of U-value?
How good a material is at insulating
Why would you want an object to emit radiation?
To give maximum rate of energy transfer to surroundings
What is meant by efficiency?
The amount of useful energy given out
Why is trapped air a good insulator?
There are no convection currents
How do thermometers work?
Temperature increase causes the particles to gain energy and move more, therefore the liquid expands and rises up the thermometer
How can a thermogram detect injuries in the body?
~ It will show the area as red
~ The area will be red due to it being inflamed and more blood surrounding it, which makes it hotter
Why do dull/matt surfaces absorb and emit more heat than shiny surfaces?
Because lots of infrared radiation is reflected by shiny, light surfaces
What type of surface absorbs and emits the most heat fastest?
Dull, black surfaces
How can the rate of heat transfer be increased?
A greater difference in temperature between the object and its surroundings
How can the rate of heat transfer be decreased?
The use of insulation
What is conduction?
The transfer of heat energy without the substance moving
Why does steel require more heat for conduction to take place?
Because it’s particles aren’t as compact, so more energy is needed for the particles to hit each other and pass on the energy
What is condensation?
When warm gases come into contact with a cold surface, which cools the particles so that they no longer have enough energy to move as gases
What is insulation?
Covering or separating using a material. It reduces or prevents the transfer of heat, electricity and sound
What is convection?
The transfer of heat energy through movement. It occurs in liquids and gases and creates convection currents
Why does condensation cause a temperature increase?
Because particles in a gas have more energy than in a liquid. So, when a gas condensed to form a liquid, this energy is released
How does a vacuum flask reduce heat transfer?
~ Made from plastic, which is a poor insulator
Why is it a good idea to have curtains in your house?
To stop heat loss through convection
