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What is red-shift?
The idea that there is a red-shift in the light of distant galaxies because they are moving away from us and the wavelength appears longer.
What are the three methods of heat transfer?
Conduction, Convection, Radiation
What does the amount of red-shift tell you about distant galaxies?
The greater the red-shift, the faster a galaxy is moving away from us
List electromagnetic waves in order of frequency (lowest to highest)
Radio, Microwave,.Infra-red, Visible, Ultraviolet, X-Ray, Gamma
What is a transverse wave?
A wave with oscillatons at right angle to the direction travelling
What is a longtitudinal wave?
A wave with oscillations the same direction as the direction travelling
Name the common properties of all electromagnetic waves
- All travel at the speed of light
- All travel at the same speed (in a vacuum)
- All can be reflected/refracted/diffracted
- All are transverse waves
Why does refraction occur?
A wave (e.g. light) changes speed as it enters different objects so therefore the wave becomes refracted.
State the rules of refraction
- A wave going from less to more optically dense refracts towards the normal
- A wave going from more to less optically dense refracts away from the normal
When does diffraction occur?
When a wave goes through a gap which is a similar size to its wavelength
Name ways in which heat transfer can be reduced in a house
- Cavity wall insulation
- Double glazed windows
- Fibre glass insulation (loft insulation)
- Silver (shiny) paper behind radiators
Name ways in which a vacuum flask is designed to reduce heat transfer
- Silver colouring
- Vacuum between liquid and container
- Plastic cap
- Double walled container
- Plastic support
What is the only method of heat transfer that can occur in a vacuum?
Why can't conduction or convection occur in a vacuum
No particles and both methods require the movement of particles to work
How does conduction occur?
Particles are heated and vibrate more vigourously, colliding and sending the heat through and object
Why is air a poor conductor of heat?
Particles are far apart
Why are metals good conductors of heat?
Free electrons which can quickly carry heat through the metal
How does convection occur?
Uses convection currents and the idea of thermal equilibruium. As some particles are heated, they become less dense and rise and more dense, colder particles flow to replace them
What does convection occur in?
Fluids (air and liquids)
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of an object by 1 degree celsius
What does the U-Value tell you about how good an insulator something is?
The lower the U-Value, the better an insulator something is.
What is the big bang theory?
Theory that at one point, all matter in the universe was at one small point and then some sort of explosion caused the universe to be continually expanding outwards.
What is background microwave radiation?
Evidence that supports an expanding universe because the big bang initally produced small gamma rays but they've been stretched in to longer microwaves.
What electromagnetic waves can be used in cooking?
What radiation do all objects emit?
What objects are the best emitters and absorbers of infra-red radiation?
Black, dull surfaces
What electromagnetic waves can be used in optical fibres?
Infra-red and Visible
Name factors that affect the rate of evaporation
- Surface area
What is evaporation?
When particles gain heat from their surroundings and turn in to a gas before reaching their boiling point
(sweat particles gain heat from the body)
What factors affect heat quantity?
What is the law of conservation of energy?
Energy cannot be created or destroyed, it can only be transferred from one state to another.
What happens to waste energy?
It is transferred to the surroundings and becomes increasingly spread out and useless for further energy transformations
What is the National Grid?
A system of cables and transformers that provide electricity
What do step-up transformers do?
Increase the voltage and decrease the current, which reduces energy lost as electricity is transferred over long distances in cables.
What do step-down transformers do?
Decrease the voltage so electricity can safely be supplied to homes (at around 230V)
What are the advantages of overhead cables?
- Less chance of interference from nature (animals/plants)
- Easier to set up
- Can be used efficiently
How does nuclear energy produce electricity?
Nuclear fission that produces heat as a radioactive uranium atom splits. This produces heat that can turn water in to steam, drive a turbine and a generator.
What are the advantages of nuclear energy?
- No greenhouse/pollutant gases released
- Very efficient in producing energy
- Short start-up time
What are the disadvantages of nuclear energy?
- Unsightly stations
- Produce radioactive waste that has to be carefully stored for a long time
What are the two different units for E=Pxt
- E (Joules) = P(Watts) x t (Seconds)
- E (Kwh) = P (kw) x t (hours)
What is condensation?
When particles gain energy from their surroundings and turn from a gas in to a liquid.
What images does reflection produce?
Virtual, laterally inverted
What is decommisioning?
The removal of materials from (nuclear) power stations and the stoppage in their production of energy
What effect does decomissioning have on prices of energy?
It increases the prices
What is the way of working out the cost of energy?
Cost = Cost per unit x Number of units (kwh)
What is power?
Rate at which energy is transferred (energy transferred per second)
What is the formula of power?
Power = work done / time
What are the dangers of ultraviolet radiation?
Too much can damage skin cells or kill skin cells and cause cancer
What are the dangers of microwaves?
Could disrupt water molecules in body and heat human body from inside, causing death
What waves aren't refracted by the atmosphere?
Why do microwaves cook quicker than normal waves?
- Disrupt water molecules
- Cook from inside as well as outside
- Cook by convection and conduction (rather than just conduction)
What are the dangers of X-Rays
- Low doses could cause cell mutation
- High doses could kill cells