physics

• types of energy stores:

  -thermal

  -kinetic

  -gravitational potential

  -elastic potential

  -chemical

  -electrostatic

  -nuclear

  -magnetic
• energy can be transferred by heating or through work done.

  -work can be done when current flows (works is done against a resistance in a circuit) or by a force moving an object.
• kinetic energy is movement of energy

  -energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down. this is dependable on the objects mass and speed. the greater the mass and the faster, the more energy there will be in the kinetic energy store.

  equation:

  Ek= 1/2mv (squared)

  kinetic= mass, speed
• gravitational energy is a raising of energy.

  -lifting an object in a gravitational field requires work. this causes a transfer of energy to the gravitational potential energy store of the raised object. the higher the object, the more energy that is transferred. this is dependable on the objects mass, height and strength.

  equation:

  Ep= mgh

  gravitation potential= mass, field strength, height
• elastic potential is the stretching of energy.

  -stretching or squashing an object can transfer energy to its elastic potential store. so long as the limit of proportionality has not been exceeded, energy in the elastic potential energy store of a stretched spring can be found through...

  equation:

  Ee=1/2ke (squared)

  elastic potential= spring constant, extension.
• specific heat capacity:

  -the energy required to raise one kilogram (kg) of the material by one degree Celsius (°C).

  -materials that need to gain lots of energy in their thermal energy stores to warm up also transfer loads of energy when they cool down again. they can store a lot of energy.

  equation:

  change in thermal energy= mass x specific heat capacity x temperature change
• specific heat capacity practical:

  -get block of material with two holes in it (for heater and thermometer)

  -measure the mass of block and wrap it with insulating material.

  -measure the initial temperature of the block and set the P.D, of the power supply to 10 V. turn the power supply on and start a stop watch
• specific heat capacity practical:

  -when powers on, the current in the circuit does work on the heater which transfers energy from power supply to the heaters thermal energy store. the materials temperature would increase.

  -take readings of temperature and current every minute

  and you should find the current through the current doesn't change.
• energy can be transferred usefully, stored or dissipated but can never be created or destroyed.
• power is the rate of doing work:

  this is the rate of energy transfer or the rate of doing work. power is measured in Watts.

  equation:

  P= E/T or W/T

  power= energy transferred/ time

  power= work done/time
• reducing unwanted energy transfers:

  lubrication reduces frictional forces. this can reduce friction between the objects surfaces when they move, they can flow easily between objects.
• reducing unwanted energy transfers.

  -conduction and convection

  -when object is heated the energy is transferred into kinetic energy of its particles. when they collide the energy is transferred between the particles (this is conduction)

  -thermal conductivity is the measure of how quickly energy is transferred through materials in this way. higher thermal conductivity means a faster rate.

  -because liquids and gases can flow the warmer and less dense region will rise above denser, cooler regions. so energy particles move away from hotter to cooler (convection)
• reducing unwanted energy transfers:

  -thermal insulation

  -have thick walls, which makes the building Coll slowly due to having low thermal conductivity.

  -loft insulation can reduce convection currents

  -double glazed windows have an air gap between glass to prevent energy transfer by conduction

  -cavity walls have an air gap to reduce energy transferred by conduction.
• efficiency

  -useful output energy transfer/total input energy transfer

  or

  -useful power output/total power input

  -the less energy thats wasted, the more efficient the device is.
• non-renewable energy resources will run out one day.

  -fossil fuels and nuclear fuel. these are typically burnt to provide energy

  -coal

  -oil

  -gas
• renewable energy resources will never run out

  -the sun

  -wind

  -water waves

  -hydro electricity

  -biofuel

  -tides

  -geothermal
• wind power: (wind turbines)

  -these rotated blades turn the generator and produce electricity.

  -theres no pollution apart from when they're manufactured

  -effect peoples views.

  -can be noisy
• solar cells/panels:

  -generate electrical current through sunlight. these are the best cells to charge batteries etc.

  -can be cost effective but not effective in cloudy countries

  -cannt increase the power output

  -initial costs are high but energy is free and running costs are nil
• geothermal powers-

  -possible for volcanic areas or where hot rocks lie near to surface.

  -this is free and reliable that does little damage

  -can generate electricity or heat building

  -arent very many suitable locations for power plants
• hydro-electric power uses falling water:

  -requires the flooding of a valley by building a big dam. water is allowed out through turbines. there is no pollution.

  -big impact on environment due to the flooding of the valley such as rotting vegetation releasing methane and CO2 and potential loss of habitat.

  -gives an immediate response to increased demand of electricity.
• wave power:

  -need loads of wave powered turbines located around coasts.

  -no pollution but disrupts seabeds and marine habitats.

  -unreliable since waves tend to die out when wind drops.

  -initial costs are high but no fuel costs and minimal running costs.
• tidal barrages:

  -tides are used to generate electricity.

  -these are big dams build across river estuaries with turbines I them. as tide comes in it fills up and the water is allowed out through turbines at controlled speed,

  -gravitational pull of sun and moon

  -no pollution by prevents free access for boats and spoils views.

  -pretty reliable
• bio-fuels are made from plants and waste.

  -can be solid, liquid or gas and can be burnt to produce electricity or run cars.

  -carbon neutral

  -loss of species as forests have been cleared to grow bio-fuels.
• non-renewables are reliable but can create environmental problems:

  -coal, oil and gas release CO2 into atmosphere which adds to greenhouse effect and contributed to global warming.

  -can cause acid rain due to sulphur dioxide being released.

  -nuclear powers clean but the waste is very dangerous.
• current is the flow of electrical charge (electrons)

  -this electrical charge will only flow around a complete circuit if their is a P.D. the unit of current is amps(A)

  -potential difference(V) Is the driving force that pushes the charge around.

  -resistance is anything that slows the flow down (ohm)
• the greater the resistance across a component, the smaller the current that flows (for a given potential difference across the component)
• circuit diagram symbols

  A) cell

  B) battery

  C) diode

  D) resistor

  E) LED

  F) lamp

  G) fuse

  H) voltmeter

  I) ammeter

  J) thermistor

  K) LDR

  
• potential difference (V)= current (A) x resistance 9ohms)
• ammeter measures the current in amp flowing through the test wire. it MUST always be places in series.
• Voltmeter measures the potential difference across the test wire. it MUST always be placed in parallel
• I-V characteristic refers to a graph that shows how the current flows through a component shares as the P.D across it is increased.
• I-V characteristics.

  A) ohmic

  B) filament

  C) diode

  
• LDR- is short for light dependent resistor. this is dependent on intensity of light.

  in a bright light, the resistance falls, the darkness means the resistance is at its highest.
• thermistor- is a temperature dependent resistor. in hot conditions the resistance drops but in cool conditions the resistance goes up.
• potential difference is shared. they always add up to equal source potential difference.
• current is the same everywhere. the size of the current is determined by the total potential difference of the cables and the total resistance of the circuit.
• main supplies for electricity:

  -alternating current (ac) and direct current (dc)

  -in AC, the current constantly changes direction and are produced by alternating voltages.

  -we have 230 V in our supplies.

  -frequency of AC is 50 cycles per second (50Hz)

  -direct current is a current thats always flowing in the same direction.
• cables have three wires that have a core of copper and a coloured plastic coating:

  -live wire: brown (provides alternation p.d of 230V from mains supply)

  -earth wire: green and yellow (stops appliance casing from becoming live. doesn't usually carry current only at fault it does)

  -neutral wire: blue (completes the circuit. when operating the current flows through live and neutral)
• national grid:

  -a giant system of cables and transformers that covers the UK and connects power stations to consumers.

  -transfers electrical power from power stations to anywhere on the grid.
• national grid:

  -transmits huge amount of power needed, you need either a high potential difference or high current

  -however having a high current is that you can lose loads of energy as wires heat up and go to surroundings.

  -its cheaper to boost pd really high and keep the current as low as possible.