Physics P1

• All objects emit and abosrb infrared radiation
• The hotter an object is, the more infrared readiation it radiates in a given time
• Dark, matt surfaces are good abdorbers and good emitters of infrared radiation
• Light, shiny surfaces are bad emitters but good reflectors of infrared radiation

Conduction in metals:

• In metals, there is a free delocalised electron which makes it a good conductor of heat and electricity
• This is because as the metal gets hotter, the tightly packed particles gain more kinetic energy and vibrate, this transfers energy to the cooler parts of the metal via delocalised electrons that move freely through the metal and collide with other particles

Conduction in non-metal solids:

• The particles pass energy from one electron to the other, however due to lack of delocalised fee elcectrons, most non-metals are bad conductors of hest and energy
• Gases are bad conductors too because of how far apart the particles are

THERMAL CONDUCTOR= conduct heat e.g. metal 

THERMAL INSULATOR= do not conduct heat or let it pass through e.g. platic, wood

CONVECTION= tranfer of heat energy through movement. Occurs in liquids and gases and created convection currents

• In iquid and gases, the particles near the heat source move faster and become further apart; causes the substance to expand and bcome less dense than the cooler parts
• Then the warm liquid or gas rises up and the colder, denser liquid or gas moves into the space crated (near the heat source)

CONDENSATION= chnage of gas into a liquid

EVAPORATION= change of liquid into a gas

Factors increasing rate of evaporation and condensation:

• increase in surface area of liquid
• air moving over surface of liquid

Condensation rate is increased if temerature is decreased

Evaporation rate is increasd if temperature is increased

Rate at which heat is transferred relies on a number of factors:

• Large surface area:volume ratio =lose heat quicker, but smaller surface area:volume ration will minimise heat lose
• Different materials transfer heat at different rates= fur, feathers and clothes are poor conductors to reduce heat loss and trap air too
• Sweat or dogs panting evaporates off the surface taking heat from the surounding with it
• The surface that the object is in contact with
• The bigger the temperature difference between and object and its surroundings, the faster it transfers heat
  

Car Radiators and Cooling Fins

Car radiators are black so radiate heat well and have a large SA due to small cooling finsa

Vacuum Flasks

They reduces heat loss both ways, so hot stays hot vica versa. Flasks are normally plastic which is a poor conductor. The shiny sides reflect infrared radiation and stop heat transfer. Vacuum has no particles so convection and conduction can't take place. Screw prevents evaporation and convection current

U-values:

• a measure of how affective a material is as an insulator
• the lower the U-value the better the material is as an insulator

Specific Heat Capacity:

Energy Transferred (J) = Mass (Kg) X Specific heat capacity (J/Kg C) X Temp change ( C)

• Specific heat capacity is useful for deciding which materials to use in heatin and cooling applications
• For example, water has a high specific heat capacity so it can store a lot of heat energy without getting too warm- useful as a coolant
• Water is also in solar heating panels. Water-filled panels placed on a roof absorb heat from the sun, this radiation warms the water. The water in the panel store a lot of heat energy which can be used to heat buildings or provide domestic hot water
• Solar panels are black and have a large surface area to absorb as much infrared energy as possible

Payback time= total cost of improvement / savings per year

• Heat loss via roof can be prevented by roof insulation which traps layers of air between fibres or insulating material. The benefits are reduced heat loss by 20-25% and short payback time. However the problems are that it requires safety precautions e.g. wearing dust masks and gloves
• Heat can also be lost under doors and windows but can be prevented by draught excluders which keep in as much air as possible. The benefits are that heat loss is reduced up to 15%, it is also cheap and easy to install with a short payback time. However the problems are that you must make sure that air vents aren't blocked becuase fresh air needs to ciruculate to prevent dry rot
• Heat can be lost from walls wwhich can be prvented by cavitiy wall insulation and internal thermal boards, This reduces heat loss up to 35% however the problems are that it is expensive and long payback time
• Heat loss from windows can be prvented by using double glazing which traps air between 2 glass sheets or curtains which stops heat loss through convection. Benefits are that double glazing reduces up to 10% heat loss and cutains are cheap and easy to install. However double glazing is expensive and long payback time
• Floor heat loss can be prevented with carpets, rugs and underfloor insulation to stop 15 of heat loss through the floor, carpet and rugs are also easy to install however underfloor nsulation is expensive and has a long payback time

• Energy can be usefullt transferred, stored or dissipated, but CANNOT be created or destroyed
• When energy is transferred, only some of it is usefully transferrd, the rest is waste
• Wasted energy is eventually transferred into the surroundings which become warmer, the wasted energy spread out and become less useful

The bend is the wasted energy

The thicker the arrow, more energy it represents

Most energy transferrd to homes and industries are electrical energy which is easily transformed into:

• thermal (heat) energy e.g. and electric fire
• light energy e.e lamp
• sound energy e.g. stero speakers
• kinetic (movement) energy e.g. an electric whisk

The amount of energy an appliance transfers is based on how long the appliance has been switched on an its' appliance

power= kilowatts (kW) or watts (W)

energy transferred= kilowatt-hours (kWh) or joules (J)

time= hours (h) or seconds (s)

By using the energy transferred equation in kilowatt-hours, you can find the cost of the energy transferred from the mains using this equation:

Total Cost= Number of kilowatt hours X Cost per kilowatt hours 

Non-renewable sources used to generate electricity include:

• Fossil fuels (coal, oil and gas) which are burnt to heat water/ air
• Nuclear fuels (uranium, plutonium) where the energy relased during nuclear fission is used to heat water

Renewable sources to generate electricity:

• Examples include biofuels, turbines, solar panels, hydroelectric dams, tidal barrage, nodding duck, geothermal
• They are renewable because they will not run out as they are continuously repplaced. 
• Many generated via sun and moon
• Moon= gravitational pull creating tides
• Sun= evaporation resulting in rain and flowing water
• Sun= convection current resulting in wind which in turn create waves

Carbon Capture

• Used to deal with excess carbon dioxide from burning fossil fuels, best storage containers are oil and gas fields
• Carbon dioxide can be pumped into gas fields displacing the natural gas burnt as a fuel.
• Carbon dioxide can also be pumped into oil under pressure to make it easier to extract

Solar Furnaces

• Large scale solar production use hundreds of mirrors to reflect infrared energy from the Sun onto a tank full of water
• This energy is boiled in the water producing steam that is used to drive turbines similarly to a normal power station. Advantage is that no polluting gas is released

• Electricity is distributed from the power stations to the consumer via National Grid
• Transformers are essetial, before electricity is transmitted into the National Gird, the step-up transformer steps-up the volatage of electricity generated. The step-dowm transformer steps-down the voltaage before it is domestically consumed so it is safe to use.
• For a given power, increasing the voltage reduces the current, so when a step-up transformer increases voltage, it reduces current. The lower the current that passes through a wire, the cooler the wire stays and the less electricity wasted as heat.
• Overhead powerlines used in the countryside because cheaper installation and cross roads and rivers easily. Underground cables used in towns becauase of tall buildings and saftey

• Waves transfer energy and they can be either transverse or longtitudinal
• Transverse= EM waves and light, water ripples, waves on string, slinky spring that go up down
• Longtitudinal= soundwaves, shock waves and slinky spring being pushed at the ends
• Mechanical waves can be ither transverse or longtitudinal e.g. water, shock, spring or rope waves
• All types of electromagnetic waves travel and the same speed through a vacuum (space)
• Waves can be reflected, refracted and diffracted. Diffraction only occurs when the wavelength of the wave is in the same order of magnitude as the size of th gap or obstacle
• When waves are refracted at an interface, they change direction. However they are not refracted if they travel along the normal
• Frequency= how many waves pass a fixed point in a second, measured in hertz (Hz)
• Wavelength= the length of one complete wave measured in metres
• Amplitude= The height from the middle of the wave to the top

EM waves form a continuous spectrum

• Radiowaves- used for TV and radio (including diffraction effects)
• Microwaves-mobiles and satellite TV
• Infrared- remote controls
• Visible light- photograpy

• In transverse waves, the vibrations are perpendicular (90 degrees) to the direction of energy transfer of the waves
• In longtitudinal waves, the waves of vibration are parallel to the direction on energy transfer of the waves

Wave equation:

speed(m/s)/ velocity= frequency(Hz) * wavelength(m)

• The normal is a construction line which is perpendicular to the reflcting surface at the point of incidence
• The law of reflectiong applies to every reflected ray:

ANGLE OF INCIDENCE = ANGLE OF REFLECTION 

• The image produced in the plane mirror is a vitual image

• Occurs when a wave crosses and interface between different subtances
• Waves travel at different speeds through different mediums e.g. water, from shallow to deep or light from air to glass
• Light changes direction when is crosses interface (ie boundary between 2 transparent materials or different densities)
• If the light ray hits meets the boundary at 90 (along the normal) then direction is unchanged

• When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is called diffraction.

• The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap. For example:

  • ->a gap similar to the wavelength causes a lot of spreading with no sharp shadow, eg sound through a doorway
  • ->a gap much larger than the wavelength causes little spreading and a sharp shadow, eg light through a doorway.

• Sound waves are longtitudinal waves and cause vibrations in a medium- this can be detected as sound
• Pitch of a sound can be determined by the frequency and the loudness can be detected by the amplitude
• Echos are reflections of sound

• If a wave source (could be light/ sound/ microwave) is moving relative to an observer, there will be a change in the observed wavelength and frequency= the Doppler Effect
• When the source moves away from the observer, the observed wavelength increases and the frequency decreases. But the source moves closer to the observer, the observed wavelength decreases and the frequency increases.
• There is an observed increase in the wavelength of light from distant galaxies, the further away the galaxies, the faster they're moving and the bigger the observed increase in wavelength= red-shift
• Observed red-shift provides evidence that the earth is expanding and supports the Big Bang theory because:
• Light is red-shifted from other galaxies, shows that other galaxies is moving awwat from us
• The further away the galaxy is, the more light that is red-shifted, this is the most likely explanation that the universe is expanding, supports the theory that the universe could have started from a single explosion

• Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe. Comes from radiation that was present shortly after the begining of the universe
• It was discovered in 1960s when using a microwave detecting telescope, a faint glow is seen
• It's believed this background radiation comes from radiation that was present shortly after the begining of the universe
• The discovery of CMBR lead to the acceptance of the Big Bang Theory as it is the only theory that supports microwave background radiation