P1- Energy Transfer By Heating Flashcards
What is infrared radiation?
Infrared radiation is energy transfer by electromagnetic waves. All objects emit and absorb IR.
The hotter the object is, the more IR it is emitting.
IR can travel through a vacuum, which means it doesn’t need a medium/particles.
What are good absorbers and emitters of infrared radiation?
Dark, Matt surfaces are good absorbers and emitters of IR.
Describe a solid.
The particles in a solid are held next to each other, vibrating in their fixed positions.
Describe a liquid.
The particles in a liquid move about at random and are in contact with each other, so a liquid doesn’t have a fixed shape and can flow.
Describe a gas.
The particles in a gas move about randomly and are much farther apart (less dense) than particles in a solid or liquid.
How does conduction work?
Solids are good conductors.
In a hot solid particles vibrate more. They collide with the particles next to them, making them vibrate and the kinetic energy is passed from particle to particle.
Why are metals good conductors and non-metals bad conductors?
Metals are good conductors because they have ‘free’ electrons to carry the energy.
Non-metals are poor conductors because they do not contain free electrons.
How does convection work?
When a fluid is heated it expands, becomes less dense and rises above the denser cool fluid.
The denser cool fluid moves to take the place of the hot fluid and itself becomes heated, whilst the hot fluid begins to cool.
A convection current is formed.
What is evaporation and what does it cause.
Evaporation is when a liquid turns into a gas.
The most energetic liquid particles escape from the liquid’s surface therefore the overall kinetic energy of the liquid decreases, meaning evaporation causes cooling.
Define condensation and how can the rate of condensation be increased?
Condensation is when a gas turns into a liquid.
Rate of condensation can be increased by :
- Increasing surface area.
- Reducing surface temperature.
How can the rate of evaporation be increased?
Rate of evaporation can be increased by:
- Increasing the surface area of the liquid.
- Increasing the temperature of the liquid.
- Creating a draught of air across the liquids surface.
What does the rate of heat transfer depend on?
Rate of heat transfer depends on:
- Area (Size).
- U value (Material)(Colour).
- Temperature Difference (between object and surroundings).
How does area affect the rate of heat transfer?
The bigger the area, the greater the heat loss therefore the bigger the rate of heat transfer.
How do U-Value affect the rate of heat transfer?
The bigger the U-value the greater the heat loss therefore the bigger the rate of heat transfer.
How does the temperature difference affect the rate of heat transfer?
The bigger the temperature difference, the greater the heat loss therefore the bigger the rate of heat transfer.
How does a vacuum flask minimise heat loss?
The plastic cap stops the evaporated liquid from escaping.
There is a vacuum between the double walled glass/plastic container which prevents conduction or convection.
The inside surfaces are silver to stop radiation.
What is specific heat capacity?
The specific heat capacity of a material is the amount of energy needed to increase the temperature of 1kg of material by 1 degree Celcius.
It is measured in J/kgoC.
What is the equation for Specific Heat Capacity?
E= m x c x ø
E= Energy transferred in Joules (J).
m= Mass in kg.
c= Specific Heat Capacity in J/kgoC.
ø= Temperature Change in oC.
What is a U-value?
U-values tell us how much energy p/second passes through different materials.
The lower the U-value, the better the material is as an insulator.
How good an insulator a material is.
How can people reduce the rate of heat transfer out of their homes?
- Fibreglass loft insulation to reduces energy transfer by conduction.
- Cavity wall insulation to reduce energy transfer by convection.
- Double glazing to reduce energy transfer by conduction.
- Draught proofing to reduce energy transfer by convection.
- Aluminium foil behind radiators to reflect IR back into the room.
Explain how plastic foam between walls may reduce energy transfer by convection (2 marks).
Air is trapped in plastic foam (1).
Air cannot move to form convection currents (1).
What are bad absorbers and emitters of infrared radiation?
Light, shiny surfaces are poor absorbers and emitters, but good reflectors or IR.
What are insulators and give an example of a good one?
Poor conductors are called insulators. Materials like wool are good insulators.
What is convection?
Convection is the circulation of a liquid or gas caused by heating. In only takes place in liquids and gases (a fluid).
Energy is transferred through the metal walls of a can of drink by conduction. Explain how (4 marks).
Metals have free electrons (1), these gain kinetic energy (1). Free electrons transfer energy to other electrons (1) by collision (1).
