Physics P1

Physics P1

1. Waves 1.4

   • The nature of waves
     • We use waves to transfer energy and infomation
     • Transverse waves vibrate at right angles to the direction of the energy transfer of the waves. All electromagnetic waves are transverse.
     • Longitudinal waves vibrate parallel to the direction of energy transfer of the waves. A sound wave is an example of a longitudinal wave.
     • Mechanical waves , which need a medium to travel through, maybe transverse or longitudinal waves
   • Wave properties
     • Reflection
       • The normal at a point on a mirror is a line drawn perpendicular to the mirror
       • For a light ray to be reflected by a mirror:
         • The angle of reflection is between the reflected ray and the normal
       • The angle of incidence is the one between the incidence ray and the normal
       • Angle of incidence=Angle of reflection
     • Refraction
       • Refraction is the change in direction of waves when they travel across a boundary
       • When a wave refracts from the air into glass, the angle of refraction is less than the angle of incidence
       • When a wave refracts from glass into the air, the angle of refraction is more than the angle of incidnece
     • Diffraction
       • Diffraction is the spreading out of waves when they go through gap or around the edge of an obstacle
       • The narrower the gap the greater the diffraction is.
       • If radio waves do not diffract enough when going over a hill , radio and TV reception wil be poor
   • Sound
     • The frequency range for the normal human ear is from 20Hz to about 20000Hz
     • Sound waves are vibrations that travel through a medium. They cannot travel through a vacuum
     • Echos are due to sound waves that are reflected of a smooth, hard surface
   • Musical sounds
     • The pitch of a note increases if the frequency of the sound wave increases
     • The loudness of a note increases if the amplitude of the sound wave increases
     • The vibrations created inside an instrument when it is played produce sound waves

2. Generating energy 1.3

   • Electrical Appliances
     • Can turn electrical energy into useful energy at the flick of a switch
     • Designed for a purpose and should produce as little waste energy as possible
   • Electrical power
     • Power is the rate of transfer of energy
     • P=E/t
     • Efficiency=useful energy/total energy (x100%)
   • Using electrical energy
     • A kilo =-watt hour is the amount of energy supplied to a 1 kW appliance in 1 hour
     • E=P/t
     • Total cost= Amount of kWh used/The cost per kWh
   • Cost effectiveness matters
     • Getting the best value for money
     • To compare cost effectiveness of different appliances you need to account of cost to buy it, running cost as well as environmental costs
   • Fuel for electricity
     • Electricity generators in power stations are driven by turbines
     • Coal, oil and natural gases are burnt in fossil fuel power stations
     • Uranium and plutonium are used as fuels in power stations
       • They release much more energy per kg than normal fuels
     • Biofuels are a renewable source of energy. Biofuels such as methane and ethanol are used to create energy
   • Energy from wind and water
     • A wind turbine is an electricity generator on top of a tall tower
     • Waves produce energy by turning a floating generator
     • Hydroelectricity generators work are turned by water running downhill
     • A tidal traps water at each high tide and uses it to turn generators
   • Power from the sun and the earth
     • Solar cells are flat solid cells that convert solar energy directly into electricity
     • Solar heating panels use the suns energy directly to heat water
     • Geothermal energy comes from the energy from radioactive substances occuring deep inside the earth
     • Water pumped into hot rocks underground which produces steam that drives a turbine
   • Energy in the environment
     • Fossil fuel produce a large amount of green house gases when burned which adds to global warming
     • Nuclear fuels produce radioactive waste
     • Renewable energy sources affect plants and animals
   • National Grid
     • The national grid is a network of cables and transformers that distributes electricity to our homes from distant power stations and renewable generators
     • Step-up transformers increase the power station voltage to the grid voltage.
     • Step-down transformers decrease the grid voltage down to a suitable voltage for a house
     • A high grid voltage reduces energy loss and makes the system more efficient
   • Big energy issues
     • Gas-fired stations and pumped-storage stations cam meet variations in demand
     • Nuclear, coal and oil power stations can meet base-load-demnds
     • Nuclear power stations, fossil-fuel power stations using carbon capture and renewable energy are all likely to contribute to the future

3. Electrical energy 1.2

   • Energy transfers and effeciency
     • Energy cannot be created or destroyed
       • Conservation energy
     • Only some energy is used "usefully" and most is "wasted" on things such as heat.
     • Wasted energy is eventually transferred to the surroundings, which become warmer
       • The wasted energy becomes increasingly spread out and so becomes less useful
     • Energy can change into/transfer into different types.
   • Useful energy
     • Efficiency=useful energy in divided by total energy
     • No machine can be more than 100% efficient
     • measures to make machines more efficient include reducing air resistance, air resistance, electrical resistance and noise

4. Energy transfer by heating 1.6

5. Electromagnetic waves 1.5

   • The electromagnetic spectrum in order of decreasing wave length from left to right
     • Radiowaves
       • Used for radio, TV broadcasting as well as radio communications and mobile phone calls
       • Can cause internal heating
     • Microwaves
       • Used for satellite TV and mobile home calls
     • Light
     • Ultra violet radiation
     • Gamma rays and X-ray
     • infrared radition
       • Used to carry signals remote handsets and from inside optical fibres
       • can cause skin burns
     • Wave speed equation: Wave speed m/s= frequency Hz x wavelength m
       • Used to calculate the frequency or wavelength of electromagnetic waves
   • White light contains all the colours in the visible spectrum

6. Using energy 1.1

   • Infrared radiation
     • Can be used for seeing animals in the dark. By detecting the infrared radiation it is emitting
     • The hotter the object the more infra red radiation
     • Transferred by electromagnetic waves
     • Only short wavelength infrared rays (and light) can penetrate the green house like atmosphere of the earth and is unable to escape heating it up.
       • If the earth heats up to much it can cause many problems worldwide Eg: Ice caps melting
   • Surfaces and radiation
     • Dark, matt surfaces emit more infrared radiation than shiny light objects
     • Dark, matt surfaces absorb more inrfrared radiation than shiny light surfaces
     • Shiny,light surfaces reflect more infrared radiation than dark, matt surfaces
   • States of matter
     • A solid does not flow not flow and has a fixed shape. Its density is much higher than gas and its volume is fixed.
       • Particles in a solid are tightly packed and are unable to move.
     • Liquids do flow and fit the shape of whatever container they are in. It is much more dense than gas and its volume is fixed.
       • Particles in a liquid move about randomly but are in contact with each other
     • Gases do flow and fill the container they are in. It is much less dense than solids but its volume can be changed
       • Particles in a gas move around freely not in contact with other particles
     • Density, volume, shape and flow are the way to describe the properties of a state of matter
   • Conduction
     • Metals are the best conductors of energy
     • Materials such as wool and fiberglass make the best insulators
     • Conduction of energy in a metal is mainly due to the free electrons transferring energy inside of the metal
     • Non-metals are poor conductors because they do not contain free electrons
   • Convection
     • Convection is the circulation of a fluid caused by heating it
     • Convection only takes place inside liquids and gases
     • Heating a gas or a liquid makes it less dense causing it to rise and staring circulation
   • Evaporation and condensation
     • Evaporation is liquid to gas
     • Condensation is gas to liquid
   • Energy transfer by design
     • The rate of energy transfer depends on
       • Shape, size and type of material
       • The materials the object is in contact with
       • Temperature difference between the object and its surroundngs
   • Specific heat capictiy
     • The greater the mass of the object the longer it takes for the temperature to increase when the object is heated up
     • The rate of temperature increase depends on
       • Mass
       • The energy supplied to it
       • Specific heat capacity
   • Heating and insulating buildings
     • Ways of reducing energy transfer in buildings
       • Loft insulation
       • Double glazing
       • Cavity wall insulation
       • Aluminium foil behind radiators
     • U-values tells us how much energy passes through a material be second
     • Solar panels do not use fuel to heat water but it does cost a lot to buy and install