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Energy AQA Physics topic 1
1.1 Energy Stores and Systems 21/11/2017
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The 9 types of energy
Type 3 example sources
Heat
Kinetic (movement)
Nuclear
Sound
Light
Chemical
Electrical
Gravitational potential
Elastic potential
Type 3 example sources
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The Laws of Physics There are many laws of physics, but one of the most important ones is:
Energy cannot be created or destroyed, it can only be converted
from one form to another
21/11/2017 Energy 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
Energy Transfer Circus
Look at the following objects and write down what their energy changes are:
a) Electric Light Bulb b) Battery c) Hairdryer d) Candle Burning e) Model Car (Wind-up) f) Dynamo g) Yo-Yo h) Radio i) Kettle j) Dropping a Golf Ball
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Kinetic energy Any object that moves will have kinetic energy.
The amount of kinetic energy an object has can be found using the formula:
Kinetic energy = ½ x mass x speed squared
in J in kg in m/s
KE = ½ mv2
You need to learn this equation!!
21/11/2017 Example questions 1) Lydia drives her car at a speed of 30m/s. If
the combined mass of her and the car is 1000kg what is her kinetic energy?
2) Sam rides her bike at a speed of 10m/s. If the combined mass of Sam and her bike is 80kg what is her kinetic energy?
3) Josh is trying to catch a bus and is running at 3m/s. If he has a mass of 60kg how much kinetic energy does he have?
4) A 2000kg car is being driven at a speed of 10m/s. If it doubles its speed to 20m/s what happens to the car’s kinetic energy?
450,000J
4000J
270m/s
Increases from
100,000J to 400,000J
21/11/2017 Example questions (higher) 1) Steve is running away from the police and
has 100J of kinetic energy. If he is running at 2m/s what is his mass?
2) James is driving in his car and has a combined mass of 1200kg. If he has 540KJ of kinetic energy what speed is he driving at?
3) Dave is running and has a kinetic energy of 750J. If his mass is 60kg how fast is he running?
4) Stuart is spotted walking around Tescos. If he has a kinetic energy of 150J and he’s walking at a pace of 2m/s what is his mass?
50kg
30m/s
5m/s
75kg
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Force and Extension
Consider a mass on a spring:
When a force is applied to this spring it will change shape and extend. The spring will have “stored elastic potential energy”
What happens when a mass is added?
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Elastic Potential Energy Elastic potential energy is the energy stored in a system when work is done to change its shape, e.g:
Describe the energy changes when the mass is:
1) At the top of it’s movement
2) In the middle
3) At the bottom
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Elastic Potential Energy Task: Calculate how much stored EPE there is in your springs
Stored EPE = ½ke2
F = ke
Weight added (N)
Extension (m)
Stored EPE (J)
1
2
3
4
5
6
You DON’T need to learn this equation!!
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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 = mass x grav. field strength x Change in height
(Joules) (newtons) (N/Kg) (metres)
GPE
H mg
You need to learn this equation!!
21/11/2017 Some example questions… How much gravitational potential energy have the following
objects gained?:
1. A brick of mass 1kg lifted to the top of a house (10m),
2. A 1,000kg car lifted by a ramp up to a height of 2m,
3. A 70kg person lifted up 50cm by a friend.
How much GPE have the following objects lost?:
1. A 0.2kg football dropping out of the air after being kicked up 30m,
2. A 0.05kg egg falling 10m out of a bird nest,
3. A 1,000kg car falling off its 200cm ramp.
100J
20KJ
60J
5J
20KJ
350J
Extension questions 21/11/2017
1) Jonny decides to use a spring (spring constant = 25N/m) to fire a 20g object straight upwards. He extends the spring by 50cm and fires the object upwards. How far up would it go?
2) In the above example, how fast would the object be moving immediately after leaving the spring?
15.6m
17.7m/s
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Specific Heat Capacity This can be thought of as “the capacity of an object to store heat”. Consider some water:
If we heat this beaker up it’s fairly clear that the amount of energy it gains depends on how much water there is and how hot it gets…
Energy = mass x s.h.c x temp change
ΔE = mcΔθ
You DON’T need to learn this equation!!
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Investigating Specific Heat Capacity How can we measure SHC experimentally?
A
V 12V 1) Calculate E if E = voltage x current x time (in seconds)
2) Divide this by the mass of the water in kg
3) Divide this by the change in temperature
4) Write down your answer – specific heat capacity of water = _____J /(kg.0C)
E = VIt and E = mcΔT
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Some example questions 1) A beaker filled with 0.1kg of water with specific heat
capacity 4200J/(kg.0C) is heated from 200C to 800C. Calculate the amount of heat energy gained by the water.
2) Another beaker containing 24g of water starts at 500C. If it loses 2000J of energy what temperature has it dropped to?
25.2 KJ
30.20C
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Another way…
A
V 12V
A metal
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If you eat a pizza from a hot oven, the crust might be harmless while the cheese topping scalds your tongue. Use your ideas about specific heat capacity to explain why.
Question 1
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Using the equation E = m × c × θ… How much energy would be transferred to raise the temperature of 2 kg of water from 20°C to 30°C? The specific heat capacity of water = 4181 J/Kg/°C
Question 2
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The specific heat capacity of water is 4181 J/Kg/°C and that of lead is 128 J/Kg/°C. If you had both the same mass of lead and water which would require the most energy to heat and why?
Question 3
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Question 4
Radiators can either be filled with water or filled with oil. Water has a higher specific heat capacity. What are the advantages and disadvantages of each?
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If you eat a pizza from a hot oven, the crust might be harmless while the cheese topping scalds your tongue. Use your ideas about specific heat capacity to explain why.
Question 1
Crust has a lower SHC so the cheese holds the heat in for a longer amount of time.
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Using the equation E = m × c × θ… How much energy would be transferred to raise the temperature of 2 kg of water from 20°C to 30°C? The specific heat capacity of water = 4181 J/Kg/°C
Question 2
83,620J
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The specific heat capacity of water is 4181 J/Kg/°C and that of lead is 128 J/Kg/°C. If you had both the same mass of lead and water which would require the most energy to heat and why?
Question 3
Water would need more energy to heat up as it has a higher SHC.
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Question 4
Radiators can either be filled with water or filled with oil. Water has a higher specific heat capacity. What are the advantages and disadvantages of each?
Water would need more energy to warm up (disadvantage?) but would also take a longer time to cool down again (advantage?).
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Work done
When any object is moved around work will need to be done on it to get it to move (obviously).
We can work out the amount of work done in moving an object using the formula:
Work done = Force x distance moved
in J in N in m W
s F You need to learn this equation!!
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Example questions 1. Amy pushes a book 5m along the table with a force of 5N.
She gets tired and decides to call it a day. How much work did she do?
2. Jodie lifts a laptop 2m into the air with a force of 10N. How much work does she do? What type of energy did the laptop gain?
3. Ronnie does 200J of work by pushing a wheelbarrow with a force of 50N. How far did he push it? What type of energy did the wheelbarrow gain?
4. Julian cuddles his cat and lifts it 1.5m in the air. If he did 75J of work how much force did he use?
5. Travis drives his car 1000m. If the engine was producing a driving force of 2000N how much work did the car do?
25J
20J, GPE
4m, KE
50N
2MJ
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Energy and Power The POWER RATING of an appliance is defined as “the rate of doing work” or “the rate of transferring energy” and is measured in Watts.
In other words, 1 Watt = 1 Joule per second
W
T P
E = Energy (in joules)
P = Power (in watts)
T = Time (in seconds)
Power = work done or energy
time
You need to learn this equation!!
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Some example questions 1) 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) Georgia runs up the stairs in 5 seconds. If she transfers 1,000,000J of energy in this time what is her power rating?
4) How much energy does a 150W light bulb transfer in a) one second, b) one minute?
5) Brad’s brain needs energy supplied to it at a rate of 40W. How much energy does it need during a 50 minute (3000 second) physics lesson?
6) Gabriel’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?
60W
2KW
150J, 9KJ
120KJ
1.73MJ
0.2MW
Who is the most powerful? 21/11/2017
Aim: to find out which student is the most powerful!
Method:
1) Measure your mass in kg
2) Measure the height of a flight of stairs in the B block
3) Calculate how much GPE you would gain by running up these
steps (g=10N/kg)
4) Time how long it takes you to run up the steps
5) Work out your power rating!
1.2 Conservation and Dissipation of Energy
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The Laws of Physics Recall one of the most important laws of Physics:
Energy cannot be created or destroyed, it can only be converted
from one form to another
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Conservation of Energy In any energy change there is ALWAYS some “waste” energy:
e.g. a light bulb:
In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use.
Electricity Light + heat
Describe the following energy changes and state the “waste” energy or energies:
1) A vacuum cleaner
2) A TV
3) A dynamo/generator
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Heat Loss from a House
House Insulation Research 21/11/2017
Task: Find out answers to the following: 1) How are houses commonly insulated? List at least 4
methods
2) Find a picture of each of these methods
3) Arrange these methods in order of: a) How much they cost to install b) How effective they are (i.e. how much money they
might save you) c) Their “thermal conductivity” – i.e., how much heat
energy goes through them
21/11/2017 Efficiency Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it.
For example, consider a TV:
Electrical Energy (200J) Sound (40J)
Efficiency = Useful energy out
Energy in x100%
You need to learn this equation!!
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Some examples of 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?
1) A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it?
2%
60%, given out to the
surroundings as heat
40,000J
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Which bulb is an energy efficient one?
Increasing Efficiency (HT only) Earlier on in this unit we considered these energy
changes. How could we increase the efficiency of these devices?
a) Electric Light Bulb b) Battery c) Hairdryer d) Candle Burning e) Model Car (Wind-up) f) Dynamo g) Yo-Yo h) Radio i) Kettle j) Dropping a Golf Ball
1.3 – National and Global Energy Resources
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Fuels A “fuel” is something that can be burned to release heat and light energy. The main examples are:
Coal, oil and gas are called “fossil fuels”. In other words, they were made from fossils.
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Renewable and non-renewable sources
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, which is non-renewable but NOT a fossil fuel.
A renewable energy source is clearly one that can be _______ (“renew = make again” or “replenish”), e.g. _____, solar power etc.
Words – non-renewable, coal, fossil fuels, wood, renewed
Q. What do we use energy sources for? Why do we need them?
The problem with fossil fuels… 21/11/2017
21/11/2017 Pollution
When 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
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Non-renewable energy sources
Coal, oil, gas and nuclear
Advantages Disadvantages
Cheap fuel costs
Good for “basic demand”
Fuel will run out
Pollution – CO2 leads to global warming and SO2
leads to acid rain
Reliable
Nuclear produces little pollution
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Renewable Sources of Energy- Biomass
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Wind Power
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Tidal Power
High tide
Low tide
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Wave Power
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Hydroelectric Power
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Solar Panels and Thermal Towers
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Geothermal Energy
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Renewable energy sources summary
Wind, tidal, hydroelectric and solar
Advantages Disadvantages
Zero fuel costs
Can be replenished/ won’t run out
Don’t produce pollution
May involve damaging the local environment
Unreliable (except for
hydroelectric)
Expensive to build
Solar is good for remote locations (e.g. satellites)
21/11/2017
Energy Supply in the UK What conclusions can you draw from the following information?
What good or bad points can you draw from this information?
