 # Energy.

## Presentation on theme: "Energy."— Presentation transcript:

Energy

The ULTIMATE energy source
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

Gravitational potential
The 9 types of energy Type 3 example sources Type 3 example sources Heat Kinetic (movement) Nuclear Sound Light Chemical Electrical Gravitational potential Elastic potential

Electricity Light + heat
Energy changes To describe an energy change for a light bulb we need to do 3 steps: 1) Write down the starting energy: 3) Write down what energy types are given out: 2) Draw an arrow Electricity Light + heat What are the energy changes for the following…? An electric fire A rock about to drop An arrow about to be fired

Conservation 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.

Heat and Temperature Heat is a type of energy that will flow from a warm area to a colder one. For example… 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. Words to use – giving out, warm up, taking in, cool down

Words – vibrations, electrons, solid, heated, better
Conduction 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. Words – vibrations, electrons, solid, heated, better

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

Some questions on convection…
Freezers in supermarkets are often left open to the air. Explain why the food does not melt easily. Explain why a hot air balloon rises in the air. Explain why an ice cube floating at the top of a drink will cool all of the drink.

Radiation 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 cool! I’m very hot!

Radiation NOTES 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 ___. 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

Cavity wall insulation
House insulation Loft insulation Cavity wall insulation Double glazing Draught excluders

In other words, 1 Watt = 1 Joule per second
Energy and Power The POWER RATING of an appliance is simply how much energy it uses every second. In other words, 1 Watt = 1 Joule per second E T P E = Energy (in joules) P = Power (in watts) T = Time (in seconds)

Some example questions
What is the power rating of a light bulb that transfers 120 joules of energy in 2 seconds? What is the power of an electric fire that transfers 10,000J of energy in 5 seconds? Farhun runs up the stairs in 5 seconds. If he transfers 1,000,000J of energy in this time what is his power rating? How much energy does a 150W light bulb transfer in a) one second, b) one minute? Shaun’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a physics lesson? 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?

Calculating the cost of electricity
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: 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

Gravitational Potential Energy
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 H W

Some example questions…
How much gravitational potential energy have the following objects gained?: A brick that weighs 10N lifted to the top of a house (10m), A 10,000N car lifted by a ramp up to a height of 2m, A 700N person lifted up 50m by a ski lift. How much GPE have the following objects lost?: A 2N football dropping out of the air after being kicked up 30m, A 0.5N egg falling 10m out of a bird nest, A 10,000N car falling off its 2m ramp. Mr Richards when bungi-jumping off a 110-metre high bridge in Zambia in August

Efficiency 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%

Some examples of efficiency…
5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it? 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? A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it?

Energy 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: “Input” energy “Output” energy 20 J/s light energy 100 J/s electrical energy 80 J/s heat energy (given to the surroundings)

Example questions Consider a computer: Consider a kettle:
150 J/s electrical energy 10 J/s wasted sound 20 J/s wasted heat Useful light and sound How much energy is converted into useful energy? What is the computer’s efficiency? Consider a kettle: Work out each energy value. What is the kettle’s efficiency? Sound energy Wasted heat Heat to water 2000 J/s electrical energy

Renewable vs. non-renewable fuels
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

Pollution When a fuel is burned the two main waste products are _____ dioxide and ________ dioxide. Carbon dioxide destroys the ____ layer and helps to cause the _______ ______. Sulphur dioxide, when dissolved in ________, causes ______ _____. Words – sulphur, ozone, carbon, acid rain, greenhouse effect, rainwater

Power stations Generator Turbine Cooling tower Transformer Boiler

What does each part do? The boiler is where the fuel is burnt to boil water The steam from the boiler is used to turn a turbine The turbine is connected to the generator, which acts like a dynamo – it generates electricity out of movement The steam is cooled down and turned back into water in the cooling tower

Nuclear power stations
These 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”

Relatively cheap Reliable Coal, oil and gas Relatively easy to find Flexible in meeting demand Don’t produce as much pollution Nuclear Cheap fuel costs

The problems… So what’s the solution?
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?

Other ways of generating electricity…
Can we drive the turbine DIRECTLY?

Other ways of generating electricity…
Wind Hydro-electric Wave Tidal

What are the disadvantages of these renewable forms of energy?
Source Disadvantages Wind Wave Tidal Hydroelectric

Source Disadvantages Wind Wave Tidal Hydroelectric
Depends on weather, visual pollution, difficult to “store” Wave Harms wildlife, depends on size of waves, depends on weather Tidal Depends on size of tides, harms wildlife, visual pollution Hydroelectric Habitats can be destroyed, only good as a “short term” supply Also, these sources all have high setting up costs

Words – dilute, radioactive, free, satellites, light
Other options… Geothermal energy – water is heated using heat given off by _________ rocks underneath the surface of the Earth Solar energy – using solar panels ______ can be converted straight into electricity 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

Matching supply and demand…
Hydroelectric power station might “kick in” here “Baseline” power stations

Summary Renewable sources of energy are cheaper, cleaner and will not run out. However, they are incapable of providing all the energy we need, so we will have to go on burning fossil fuels for now.

Topics we’ve covered… The nine types of energy
Conduction, convection and radiation House insulation Working out energy, power and time Working out the cost of electricity Working out weight and GPE Working out efficiency How a power station works Definitions and examples of renewable and non-renewable Advantages and disadvantages of renewable and non-renewable How geothermal and solar sources work