Physics Gcse Unit 1 Aqa

1. Energy transfer by heating * Infrared Radiation * Surfaces and Radiation * States of matter * Conduction * Convection * Evaporation and condensation * Energy Transfer by design * Specific heat capacity * Heating and insulation buildings

2. Using Energy * Forms of energy * Conservation of energy * Useful energy * Energy and efficiency

3. Electrical Energy * Electrical Appliances * Electrical Power * Using electrical energy * Cost effectiveness matters

4. Generating Electricity * Fuel for electricity * Energy from wind and water * Power from sun and earth * Energy and the environment * The National Grid * Big Energy issues

5. Waves * The nature of waves * Measuring waves * Reflection * Refraction * Diffraction * Sound * Musical Sound

6. Electromagnetic Waves * The electromagnetic spectrum * Light, infrared, microwaves and radio waves * Communications * The expanding universe * The Big Bang

1: Infrared Radiation * Infrared radiation is in the electromagnetic spectrum just beyond visible red light. * Can be detected with our skin (makes us warm) * All objects emit infrared radiation * The hotter an object, the more infrared radiation emitted in a given time * Can travel through a vacuum, this is how we get energy from the sun

Surfaces and Radiation * Dark matt surfaces are good absorbers of infrared radiation. If left in the sun it will become hotter that a shiny white surface * Dark matt surfaces are good emitters of infrared radiation. It will transfer energy and cool down quicker than a shiny white surface, * Light shiny surfaces are good reflectors of infrared radiation.

States of Matter * Change between the 3 states of matter (solid, liquid and gas) occur by heating or cooling.

* Particles vibrate round a fixed point

* Fixed shape

* Particles remain in contact but move at random

* Can flow

* Far apart * Move at random much faster * Flows * Less density that liquid and solid

Conduction * Occurs mainly in solids * Mos liquids and gases are poor conductors

This energy is passed to neighbouring particles.

The energy is transferred through the solid.
One end of solid is heated, particles gain kinetic energy.

* This process occurs in metals * Metals have free electrons that gain kinetic energy and move through the metal, transferring kinetic energy by colliding with other particles. This is why they are good conductors. * Poor conductors are called insulators * Wool and fibreglass are good insulators because they contain trapped air

* Convection

Convection occurs in fluids (liquid and gas)

As hot air rises, cool air replaces it.
When a fluid is heated it expands becomes less dense and rises.

* Convection currents are responsible for onshore and offshore breezes
Evaporation and Condensation
Evaporation:
* When a liquid turns into a gas * Causes cooling * The most energetic liquid molecules escape from the liquids surface * Average kinetic energy of molecules is less * So the temperature decreases (more kinetic energy – more heat)
Rate of evaporation increased by: * Increasing surface area of liquid * Increasing the temperature of liquid * Creating a draught of air across the liquids surface
Condensation:
* When a gas turns to a liquid, often takes place on cold surfaces eg windows & mirrors
Rate of evaporation increased by: * Increasing surface area and temperature
Energy Transfer by Design * The grater the temperature difference between an object and its surroundings the greater the rate at which energy is transferred * The rate of which energy is transferred also depends on : * The materials the object is in contact with * The objects shape * The objects surface area * Maximising the rate of energy transfer keeps things cool, to do this we may use things that: * Are good conductors * Are painted dull black * Have the air flow around them maximised * Minimising the rate of energy transfer keeps things cool, to do this we need to use things that minimise the transfer of energy by conduction, convection and radiation. We may use things that: * Are good insulators * Are white and shiny * Prevent convection currents by trapping air in small pockets

Specific Heat Capacity * The specific heat capacity of a substance is the amount of energy required to raise the temperature of one kg of the substance by 1°C * Different substance have different specific heat capacities * The greater the specific heat capacity, the more energy required for each degree temperature change * E.g. the specific heat capacity of copper is 490J/Kg°C, so to raise the temperature by 1°C of 1 Kg of copper you need to use 490J * The greater the mass of a substance being heated the more energy requires for each degree temperature change. * The equation for specific heat capacity is: E = m x c x θ * E = energy transferred, J * m = mass, Kg * c = specific heat capacity, J/Kg°C * θ = temperature change,°C

Heating and Insulating Buildings * To minimise the rate of energy transfer out of homes to reduce fuel bills can be done by: * Fibreglass loft insulation, reduce energy transfer by conduction * Cavity wall insulations traps air in small pockets, reduce energy transfer by insulation * Double glazing, reduce energy transfer by conduction * Draught proofing , reduce energy transfer by convection * Aluminium foil behind radiators to reflect infrared radiation back into the room * The U-value of a material tells us how much energy passes through it per second. * The lower the U-value the better material is as an insulator * Solar heating panels contain water that is heated by the suns radiation, can be used to heat building & provide hot water. * But they are expensive to buy and install & the water is not heated at night

2: Forms of Energy * Energy exists in different forms * Energy can be transferred from one form to another * Any object above ground has gravitational potential energy * A falling object transfers gravitational energy to kinetic energy

Conservation of Energy * Impossible to create or destroy energy * Only possible to transfer it from one form to another or one place to another * Total amount of energy is always the same, this is called conservation of energy and it applies to all energy transfers * E.g. stretching an elastic band transfers elastic potential energy to kinetic energy

Useful Energy * A machine is something that transfers energy from one form/place to another * The energy we get out of machine consists of: * Useful energy, which is transferred to the place/form we want * Wasted energy, which is not usefully transferred * Useful and wasted energy will eventually be transferred to their surroundings and warm them up. As energy spreads out it is more difficult to use for further energy transfers * Energy is often wasted due to friction, this energy warms machine & surroundings * Friction can be useful e.g brakes
Energy and Efficiency * All forms of energy are measured in Joules (j) * Energy supplied to a machine is called input energy input energy= useful energy transferred + energy wasted * The less energy wasted in a machine the more efficient it is efficiency = ( useful energy transferred ÷ energy supplied ) × 100 * No appliance is 100% efficient except an electric heater * Energy transfer through an appliance can be showed with a sankey diagram

Useful energy

Total input energy

Wasted energy

Energy and Efficiency * Electrical appliances transfer electrical energy into whatever form of energy we need. * Many electrical appliances transfers energy by heating * This may be useful e.g a kettle but energy is often wasted * Appliances should be designed to be as efficient as possible

Electrical Power * The power of an appliance = the rate it transfers energy * Power is measured in watts (W). * An appliance with a power of 1W transfers 1J/s * 1 Kilowatt (kW) = 1000 watts * Power (W) = energy (J) ÷ time(s) for the energy to be transferred

Using Electrical Energy * Joules are to small to measure electricity bills instead we use Kilowatt-hour (kWh) * A Kilowatt-hour (kWh) is the amount of energy transferred by one kilowatt appliance used for one hour * The amount of energy transferred to a mains appliance can be found using the equation: E = P x t * E is energy transferred in kWh * P is the power of appliance in kW * t is time taken in hours for energy to be transferred * An electricity metre records the number of kWh of energy used. * Previous metre reading – current reading = the electrical energy used between the readings * The cost of the electrical energy supplied is:
Total cost= number of kWh x cost per kWh * The cost per kWh is given on the electricity bill

Cost Effectiveness Matters * To compare the cost effectiveness of different appliances we must consider different costs: * Cost of buying the appliance * Cost of installing appliance * The running costs * Maintenance costs * Environmental costs * Interest charged on a loan to buy the appliance * To reduce energy bills people may buy newer more efficient appliances, or could install materials designed to reduce energy wastage * Payback time is the time it takes for an appliance or installation to pay itself in terms of energy savings * E.g. loft insulation costs £600 including installation and it saves £80 per year on the fuel bill so the payback time would be 7.5 years (600÷80)

4: Fuel for Electricity * In most power stations water is heated to produce steam which drives a turbine that turns an electrical generator that produces the electricity. * The energy can come from burning fossil fuels (coal, gas or oil) * Fossil fuels are obtained over a long period of time from long-dead biological material * Hot gas may drive the turbine directly , a gas fired turbine can be turned on very quickly * A biofuel is any fuel obtained from living or recently living biological material, they are renewable e.g. wood * In a nuclear power station the fuel used is uranium * The nucleus of a uranium atom can undergo a process called nuclear fission which releases energy * There are lots of uranium nuclei so lots of fission taking place releasing lots of energy * More energy is released per kg of uranium then fossil fuels * Nuclear power stations do not give off fossil fuels but do produce nuclear waste which is difficult to dispose of

Energy from Wind and Water
Energy from wind, waves and tides is called renewable energy because they can never be used up
Wind
* We can use energy from wind and water to drive turbines directly * In a wind turbine the wind passing over the blades makes them rotate and drive a generator.
Water
* Electricity can be produced from energy obtained from falling water, waves or tides * Hydroelectric power water is collected in a reservoir , this allows water to fall down hill and turn turbines at the bottom of the hill * Wave power uses the momentum of waves in the sea to generate electricity, the momentum drives a floating generator then the electricity is delivered to the grid system on shore by cable * Tidal Power, the level of the sea around the coastline rises and falls twice a day (tides). If a barrage is built across an estuary the water at each high tide is trapped & when the water is released to fall down to the lower sea level it drives turbines. * Pumped storage system, surplus electricity is used, when electricity is in low demand to pump water uphill the energy is stored as gravitational potential energy when it is released downhill it can transfer kinetic energy to electrical energy.

Power from the Sun and the Earth * Solar energy from the sun travels through space to the earth as electromagnetic radiation. * A solar cell is able to transfer this energy into electrical energy , each cell only produces a small amount of electricity useful to power thigs such as watches * They can also be joined to make a solar panel * Solar heating panel heats water directly from the suns energy * A solar power tower uses many mirrors to reflect sunlight onto water to heat the water and produce steam

* Geothermal energy is produced inside the earth by radioactive processes that heats surrounding rock. In suitable areas deep holes are drilled and cold water is pumped down to the rocks and is heated to produce steam.

* In few parts of the world hot water comes up to the surface naturally .

Energy and the Environment
Scientist are investigating ways to reduce environmental impact of using fossil fuels e.g. sulphur may be removed from fuel before burning. Instead of allowing CO2 into the atmosphere it can be captured and stored. Energy Resources | Advantages | Disadvantages | Coal | Bigger reserve, Reliable | Non-renewable, Produces CO2, Production of SO2, acid rain | Oil | Reliable | Non-renewable, Produces CO2, Production of SO2, acid rain | Gas | Reliable | Non-renewable, Produces CO2, Production of SO2, acid rain | Nuclear | No production of polluting gases, Reliable | Non-renewable, Produces nuclear waste, difficult to dispose of, Small risk of big nuclear accident | Wind | Renewable, No production of polluting gases, Free energy source | Needs many large turbines, Not reliable, wind does not always blow | Falling Water | Renewable, No production of polluting gases, Free energy source, Reliable in wet areas | Only works in wet and hilly areas, Damming the areas causes flooding and effects local ecology | Waves | Renewable, No production of polluting gases, Free energy source | Can be hazardous to boats, Not reliable | Tides | Renewable, No production of polluting gases, reliable always tides, free energy source | Only a few river estuaries are suitable, building a barrage affects the local ecology | Solar | Renewable, No production of polluting gases, reliable in hot countries in the day time, free energy source | Solar cells only produce a small amount of energy, unreliable in less sunny countries | Geothermal | Renewable, No production of polluting gases, Free energy source | Only economically viable in very few countries, drilling is difficult and expensive. |