Energy Transfers And Conservation Flashcards
What material is the best conductors and why?
Metals because they contain lots of free electrons. When a metal is heated, these electrons gain kinetic energy and vibrate faster. Collisions between electrons transfer energy along the metal.
Why can conduction happen in non-metals?
Although there are no free electrons, the entire ions in non-metals can still vibrate slightly faster and pass on a bit of energy.
What materials are the best insulators?
Wool and fibreglass.
What is convection?
The circulation of a fluid (liquid or gas) caused by heating it.
How does convection work?
- The fluid is heated
- The area heated gains kinetic energy and becomes less dense (because the particles move faster and take up more space)
- This rises above the more dense fluid around it
- Convection currents are created
What effect does temperature have on infrared radiation?
The higher the temperature of an object, the more infrared radiation it gives off.
Does every object emit infrared radiation?
Yes, unless they are at 0K
What is infrared radiation?
Energy transfer by electromagnetic waves.
What is evaporation?
When a liquid turns into a gas.
What is condensation?
When a gas turns into a liquid.
What causes the cooling of a liquid by evaporation?
The faster-moving particles escape from the liquid.
What factor affect the rate of evaporation?
- Surface area
- Temperature of the liquid (the hotter, the faster the rate)
- Creating a draught of air above the liquid
What factor affect the rate of condensation?
- Surface area
* Surface temperature (the cooler, the faster the rate)
Do all objects absorb infrared?
Yes
What are the properties of dark, matt surfaces with regards to infrared?
- Good emitters of heat
- Good absorbers of heat
- Poor reflectors
What are the properties of light, shiny surfaces with regards to infrared?
- Poor absorbers
- Poor emitters
- Good reflectors
What affects the rate of energy transferred?
- Shape and size (Surface area)
- Material
- Surface that the object is in contact with
- Temperature gradient between object and surroundings
What is expansion by heating?
The expansion of a substance due to increasing its temperature.
What state of matter expands the most upon heating?
Gases
How is expansion made use of?
- Radiator thermostat in a car
- Liquid in a glass thermometer
- Fitting steel tyres onto trains
- Bimetallic strips
When can expansion not be useful?
• Expansion gaps in bridges
What is conservation of energy?
The idea that energy cannot be created or destroyed.
Can energy by stored?
Yes. For example, a rubber band can be stretched to stored elastic energy.
What is useful energy?
Energy in the place we want it and in the form we need it.
What is wasted energy?
Energy that is not useful energy.
What happens to energy as it spreads out (dissipates)?
It gets less and less useful.
What is the equation for gravitational potential energy?
GPE = Weight of object x Height
Joules = Newtons x Metres
What is gravitational potential energy?
Stored energy in an object.
What is a Sankey diagram?
A diagram used to show how energy is being transferred into wasted and useful energy.
How does a Sankey diagram work?
- Length of arrows DOESN’T matter
* Width of arrows shows the proportion of energy
How is efficiency calculated?
Efficiency = (Useful energy / Total energy supplied) x 100%
Why do machines waste energy?
- Friction
- Resistance of wires creates heat
- Air resistance
- Sound
How can energy transfer be reduced in the home?
- Loft insulation
- Cavity wall insulation
- Aluminium foil behind radiators
- Double glazing
- Draught proofing
What is a U-value?
A value showing how effective different materials are as insulators. The lower the U-value, the better the insulator.
How do solar heating panels work?
They use solar energy to heat water. The panels contain liquid-filled copper pipes on a matt black plate, which are connected to a heat exchanger.
What is payback time?
The time taken to recover the up-front costs of something from savings.
