11/10/2015Energy W Richards The Weald School. 11/10/2015 The ULTIMATE energy source The sun is the ultimate source of all our energy. For example, we.

19/04/23

EnergyEnergy

W Richards

The Weald School

19/04/23The ULTIMATE energy The ULTIMATE energy sourcesource

The sun is the ultimate source of all our energy.

For example, we often get energy from beef:

BEEF comes from COWS,

COWS eat GRASS,

GRASS gets energy from the sun by PHOTOSYNTHESIS

19/04/23

The 9 types of energyThe 9 types of energy

Type 3 example sources

Heat

Kinetic (movement)

Nuclear

Sound

Light

Chemical

Electrical

Gravitational potential

Elastic potential

Type 3 example sources

19/04/23

Energy changesEnergy changes

To describe an energy change for a light bulb we need to do 3 steps:

Electricity Light + heat

1) Write down the starting energy:

3) Write down what energy types are given out:

2) Draw an arrow

What are the energy changes for the following…?

1) An electric fire

2) A rock about to drop

3) An arrow about to be fired

19/04/23

Conservation of EnergyConservation of Energy

In any energy change there is ALWAYS some “waste” energy:

e.g. a light bulb:

Electricity Light + heat

In this example HEAT is wasted – it’s given to the surroundings. Waste energy is virtually

always heat and it’s always given to the surroundings.

19/04/23

Heat and TemperatureHeat and Temperature

This cup of coffee will ____ ____ because it is _____ ____ heat energy into the surroundings.

This drink (taken out of the fridge) will _____ ___ because it is _____ ___ heat energy from the surroundings.

Heat is a type of energy that will flow from a warm area to a colder one. For example…

Words to use – giving out, warm up, taking in, cool down

19/04/23

Conduction is all about when heat is transferred through a _________. The heat is passed on by ___________ in the molecules. These vibrations get BIGGER when the solid has more ENERGY (i.e. when it is being __________).

Metals are _______ conductors than non-metals. This is because the heat is carried by free ________ that can carry the energy around the metal and give it to other electrons and ions.

ConductionConduction

Words – vibrations, electrons, solid, heated, better

View Animation

19/04/23

ConvectionConvectionConvection is all about when a gas or liquid (“fluid”) moves and carries heat with it. When the fluid is heated it ____________. This means that it will become less __________ than the colder fluid around it. Because of this the warmer fluid will try to “_______” over the colder fluid, and this is why warm air rises. This is called a convection ___________. This is how heat reaches us from the ___________ in this room.

In CONDUCTION the heat was passed on by VIBRATIONS in a SOLID

In CONVECTION the heat is passed on by the FLUID expanding, rising and

TAKING THE HEAT with it

Words to use: expands, radiators, dense, heated, current, float

19/04/23Some questions on Some questions on convection…convection…

1) Freezers in supermarkets are often left open to the air. Explain why the food does not melt easily.

2) Explain why a hot air balloon rises in the air.

3) Explain why an ice cube floating at the top of a drink will cool all of the drink.

19/04/23

RadiationRadiation

When you wear a black t-shirt on a hot, sunny day you would feel ______ than if you wore ____. This is because black _______ infrared radiation (i.e. heat) from the sun better than white does.

I’m very hot!I’m cool!

19/04/23

Some examples of radiationSome examples of radiation

19/04/23

Some examples of radiationSome examples of radiation

19/04/23

Radiation is when heat moves around in electromagnetic _________ like light does. Any hot object will emit heat radiation – the hotter it is, the more radiation it emits. This type of radiation is called __________, and too much of it will cause _________. Dark, matt colours will absorb AND emit the _____ infra-red radiation, and light, shiny colours will ________ it.

The main difference with radiation is that conduction and convection could ONLY happen in solids, liquids or gases, whereas radiation will happen through an _____ _____. This is just as well, as otherwise we wouldn’t be able to get any heat from the ___.

RadiationRadiation

Words – sun, reflect, infra-red, waves, most, empty space, sunburn

Anything HOT emits HEAT RADIATION – the hotter it is, the more infra red radiation it emits

19/04/23

House insulationHouse insulation

Draught excluders

Double glazing

Loft insulation

Cavity wall insulation

19/04/23Energy and PowerEnergy and PowerThe POWER RATING of an appliance is simply how much energy it uses every second.

In other words, 1 Watt = 1 Joule per second

E

TP

E = Energy (in joules)

P = Power (in watts)

T = Time (in seconds)

19/04/23

Some example questionsSome example questions1) What is the power rating of a light bulb that transfers

120 joules of energy in 2 seconds?

2) What is the power of an electric fire that transfers 10,000J of energy in 5 seconds?

3) Farhun runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating?

4) How much energy does a 150W light bulb transfer in a) one second, b) one minute?

5) Shaun’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a physics lesson?

6) Damien’s brain, being more intelligent, only needs energy at a rate of about 20W. How much energy would his brain use in a normal day?

19/04/23Calculating the cost of Calculating the cost of electricityelectricity

Clearly, this depends on two things: the POWER RATING of the appliance and HOW LONG you leave it on for. Electricity is measured in “units”, also called “kilowatt hours” (kWh).

To work out how much something would cost use two steps:

1) Find out how many units have been used:

No. of units = Power rating x Time appliance is on for

in kWh in kW in hours

2) Multiply the number of units by how much each one costs:

Cost of electricity = no. of units used x cost of each unit

in pence in kWh in pence

19/04/23Gravitational Potential Gravitational Potential EnergyEnergy

To work out how much gravitational potential energy (GPE) an object gains when it is lifted up we would use the simple equation…

GPE = Weight x Change in height

(Joules) (newtons) (metres)

GPE

HW

19/04/23Some example questions…Some example questions…

How much gravitational potential energy have the following objects gained?:

1. A brick that weighs 10N lifted to the top of a house (10m),

2. A 10,000N car lifted by a ramp up to a height of 2m,

3. A 700N person lifted up 50m by a ski lift.

How much GPE have the following objects lost?:

1. A 2N football dropping out of the air after being kicked up 30m,

2. A 0.5N egg falling 10m out of a bird nest,

3. A 10,000N car falling off its 2m ramp.

4. Mr Richards when bungi-jumping off a 110-metre high bridge in Zambia in August

19/04/23EfficiencyEfficiency

Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it.

Efficiency = Useful energy given out by the device

Energy put into it

e.g. if 2000 joules of electrical energy are put into a kettle and 500 joules of heat energy are gained from it, its efficiency is 500/2000 x 100% = 25%

x100%

19/04/23Some examples of Some examples of efficiency…efficiency…

1) 5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it?

2) A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go?

3) A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it?

19/04/23

Energy Transfer diagramsEnergy Transfer diagrams

Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram:

100 J/s electrical energy

“Input” energy “Output” energy

80 J/s heat energy (given to

the surroundings)

20 J/s light energy

19/04/23

Example questionsExample questionsConsider a kettle:

1) Work out each energy value.

2) What is the kettle’s efficiency?

Sound energy

Wasted heat

Heat to water

2000 J/s electrical energy

Consider a computer:

150 J/s electrical energy

10 J/s wasted sound

20 J/s wasted heat

Useful light and sound

1) How much energy is converted into useful energy?

2) What is the computer’s efficiency?

19/04/23Renewable vs. non-renewable Renewable vs. non-renewable fuelsfuels

A ________ energy source is blatantly one that can be _______ (“renew = make again”), e.g. _____, solar power etc.

A ___________ energy source is one that when it has been used it is gone forever. The main examples are ____, oil and gas (which are called ______ ____, as they are made from fossils), and nuclear fuel.

Words – non-renewable, coal, renewable, fossil fuels, wood,

renewed

19/04/23Using non-renewable fuels in power Using non-renewable fuels in power stationsstations

1) A fossil fuel is burned in the boiler

2) Water turns to steam and the steam drives a turbine

3) The turbine turns a generator

4) The output of the generator is connected to a transformer

5) The steam is cooled down in a cooling tower and reused

19/04/23

PollutionPollutionWhen a fuel is burned the two main waste products are _____ dioxide and ________ dioxide.

Carbon dioxide is a _________ ___ and helps cause _______ _________. This is produced when any fossil fuels are burned.

Sulphur dioxide, when dissolved in ________, causes ______ _____. This is mainly a problem for ___ power stations.

Nuclear power stations do not produce these pollutants because they don’t ____ fossil fuels.

Words – sulphur, coal, global warming, carbon, acid rain, greenhouse gas,

rainwater, burn

19/04/23

Nuclear power stationsNuclear power stationsThese work in a similar way to normal power stations:

The main difference is that the nuclear fuel is NOT burnt – it is used to boil water in a “heat

exchanger”

19/04/23

Start up timesStart up timesDifferent power stations have different start up times:

Gas

Oil

Coal

Nuclear

Quick

Slow

19/04/23Advantages of non-renewable Advantages of non-renewable fuelsfuels

Coal, oil and gas

Nuclear

Relatively cheap

Reliable

Flexible in meeting demand

Relatively easy to find

Cheap fuel costs

Don’t produce as much pollution

19/04/23

The problems…The problems…Power stations using coal, oil, gas or nuclear fuels can certainly whack out the energy, BUT…

Problem 1 – Fossil fuels and nuclear sources will RUN OUT

Problem 2 – Burning fossil fuels will pollute the atmosphere

Problem 3 - Nuclear plants run the risk of contamination and the cost of shutting them down (“decommissioning”) is very high

So what’s the solution?

19/04/23

Non-renewable energy sourcesNon-renewable energy sources

Coal, oil, gas and nuclear

Advantages Disadvantages

Cheap fuel costs

Short start-up time for gas and oil

Good for “basic demand”

Fuel will run out

Costs a lot of money to

decommission a nuclear plant

Pollution – CO2 leads to global warming and SO2 leads to acid rain

Reliable

Nuclear produces little pollution

19/04/23Other ways of generating Other ways of generating electricityelectricity

Can we drive the turbine directly without burning any fossil fuels?

19/04/23

Wind PowerWind Power

19/04/23

Tidal PowerTidal Power

High tide

Low tide

19/04/23

Wave PowerWave Power

19/04/23

Hydroelectric PowerHydroelectric Power

19/04/23Renewable energy sources Renewable energy sources summarysummary

Wind, tidal, hydroelectric and solar

Advantages Disadvantages

Zero fuel costs

Hydroelectric is good for a

“sudden” demand

Don’t produce pollution

Tidal barrages destroy the habitats of wading birds and hydroelectric

schemes involve flooding farmland

Unreliable (except for

hydroelectric)

Expensive to build

Solar is good for remote locations (e.g. satellites)

19/04/23Other renewable options…Other renewable options…Geothermal energy – water is heated using heat given off by _________ rocks underneath the surface of the Earth

Although renewable fuels are ____, the energy we get from them is “_______”. This means that we have to spend a lot of money on generators to make them worthwhile.

This is why solar panels are only used in small things (like calculators) or extremely remote locations (like ____________).

Words – dilute, radioactive, free, satellites, light

Solar energy – using solar panels ______ can be converted straight into electricity

19/04/23Matching supply and Matching supply and demand…demand…

“Baseline” power stations

Hydroelectric power station might “kick in” here