Topic 4 – Waves and the Topic 4 – Waves and the EarthEarth

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1) Pre-natal scanning

1) Sonar

2) Communication between animals

UltrasoundUltrasoundUltrasound is the region of sound above 20,000Hz – it can ’t be heard by humans. There are a number of uses for ultrasound:

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Pulse-Echo techniquesPulse-Echo techniquesIn pulse-echo techniques sound is reflected from an object to measure the distance to that object:

19/04/23Pulse-Echo techniques - Pulse-Echo techniques - UltrasoundUltrasound

Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object.

Words – depth, reflected, picture, medium, animals

Ultrasound is the region of sound above 20,000Hz – it can ’t be heard by humans. It can be used in pre-natal scanning, sonar techniques and as communication between _______:How does it work?

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The Maths of Pulse-EchoThe Maths of Pulse-EchoConsider shouting at a wall:

The speed of sound is given by:

x

v = 2x/t

Therefore x = vt/2

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The Maths of Pulse-EchoThe Maths of Pulse-EchoThe echo takes 0.8 seconds to return and the speed of sound in water is 1500ms-1. How deep is the water?

t/μs25

50

75

100 125 150 175 200

Use the ultrasound scan to determine the width of the amniotic sac and the width of the baby’s body. The speed of sound in the fluid is 1500ms-1 and in soft tissue the speed is 1560ms-1.

19/04/23Using an oscilloscope with ultrasoundUsing an oscilloscope with ultrasound

Consider a block of metal with a flaw:

20ms/div

Q. If the speed of the ultrasonic wave is 3,000m/s how far away is the flaw from the detector?

InfrasoundInfrasound19/04/23

Infrasound is the region of sound BELOW 20Hz (as opposed to ULTRASOUND which is above 20KHz) – it can’t be heard by humans. Some uses:

1) Communication between animals

African elephants use infrasound to communicate with other elephants many kilometres away.

2) Detecting movement in remote areas

3) Detecting volcanic eruptions and meteors

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The Structure of the EarthThe Structure of the EarthA thin crust - 10-100km thick

A mantle – has the properties of a solid but it can also flow

A core – made of molten nickel and iron. Outer part is liquid and inner part is solid

How do we know this? These facts have all been discovered by examining seismic waves (earthquakes)

19/04/23Seismic wavesSeismic wavesEarthquakes travel as waves through the Earth – we call them SEISMIC WAVES. There are two types:

P waves:1) They are longitudinal so they cause the

ground to move up and down

2) They can pass through solids and liquids

3) They go faster through more dense material

S waves:1) They are transverse so they cause the

ground to move from right to left

2) They ONLY pass through solids

3) They are slower than P waves

4) They go faster through more dense material

19/04/23Seismic wavesSeismic waves

These P waves travel through the Earth and are refracted when they pass through a medium

These P waves are being reflected at the crust

These S waves cannot travel through the outer core as they only go through solidsThe paths of these waves are

all curved because density is gradually changing

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Locating EarthquakesLocating Earthquakes

By measuring the time it takes the wave to travel to these locations the location of the earthquake can be found.

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Movement of the CrustMovement of the CrustThe Earth’s _______ is split up into different sections called ________ plates:

These plates are moving apart from each other a few centimetres every _______ due to the ________ currents in the mantle caused by the ________ decay of rocks inside the core.

Words – radioactive, crust, convection, tectonic, year

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Plate MovementsPlate Movements

Oceanic Crust

Mantle

Magma

Earthquakes and volcanic eruptions can be common here

Igneous Rock

Convection Currents

Topic 5 – Generation and Topic 5 – Generation and Transmission of ElectricityTransmission of Electricity

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Electric CurrentElectric CurrentElectric current is a flow

of charge around a circuit

Note that electrons go

from negative to positive and are “pushed”

by the voltage

-+ e-

e-

By definition, current is “the rate of flow of

charge”

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Basic ideas…Basic ideas…Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____.

Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta.

Resistance is anything that resists an electric current. It is measured in _____.

Words: volts, amps, ohms, voltage, ammeter, voltmeter

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More basic ideas…More basic ideas…

If a battery is added the current will ________ because there is a greater _____ on the electrons

If a bulb is added the current will _______ because there is greater ________ in the circuit

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Electrical PowerElectrical Power

The amount of power being transferred in an electrical device is given by: P

IVPower = voltage x current

in W in V in A1) How much power is transferred by a 230V fire that

runs on a current of 10A?

2) An electric motor has a power rating of 24W. If it runs on a 12V battery what current does it draw?

3) An average light bulb in a home has a power rating of 60W and works on 230V. What current does it draw?

Power is defined as “the rate of transferring energy” and is measured in units called “Watts” (W).

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FuelsFuelsA “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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Some definitions…Some definitions…

A renewable energy source is clearly 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, which is non-renewable but NOT a fossil fuel.

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

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Using non-renewable fuels in power stationsUsing non-renewable fuels in power stations

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

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Efficiency of Power StationsEfficiency of Power Stations

100J Boiler 85J Turbine35J

Generator30J

15J 50J 5J

Heat

Heat Kinetic

Heat Heat

Electrical

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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

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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”

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Start up timesStart up times

Different power stations have different start up times:

Gas

Oil

Coal

Nuclear

Quick

Slow

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Non-renewable energy sourcesNon-renewable energy sources

Coal, oil, gas and nuclear

Advantages Disadvantages

Cheap fuel costs

Easy to use

Generate a lot of energy

Fuel will run out

Pollution – CO2 leads to global warming and SO2 leads to

acid rain

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Renewable energy sourcesRenewable energy sources

Wind, tidal, solar etc

Advantages Disadvantages

Clean

Easily accessible

Won’t run out Look ugly

Energy is “dilute” – in other words, it’s very spread

out

Often depend on the weather – is it

sunny???

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Other ways of generating electricityOther ways of generating electricity

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

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Wind PowerWind Power

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Tidal PowerTidal Power

High tide

Low tide

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Wave PowerWave Power

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Hydroelectric PowerHydroelectric Power

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BiomassBiomass

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BiofuelsBiofuelsBiomass can be used as a fuel in a number of ways:

1) Fast-growing trees that can be ____

2) Manure or other waste that can be used to release _______ (biogas)

3) Corn or sugar cane that can be broken down in a fermenter to produce ______ like bio-ethanol.

Biofuels have two main advantages over traditional fuels – they are ______ and ________. However, they still release ______ _______.

Words – alcohols, cleaner, burnt, renewable, methane, carbon

dioxide

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Solar EnergySolar Energy

Heating for homes – these pipes carry water that absorbs heat energy and transfers it to the house.

Solar panels – convert sunlight directly into electricity. Sunlight knocks electrons loose from the crystal structure and the loose electrons form an electric current. The amount of power depends on the area of the panel and the light intensity.

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Geothermal EnergyGeothermal Energy

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Geothermal EnergyGeothermal Energy

Geothermal energy can be used in _______ areas such as ______. In a geothermal source cold water is pumped down towards ____ _____. The water turns to steam and the steam can be used to turn ______. In some areas the _____ rising at the surface can be captured and used directly.

Words – steam, Iceland, volcanic, turbines, hot rocks

19/04/23Solar Panels and Thermal Solar Panels and Thermal TowersTowers

19/04/23Using Solar Energy in remote Using Solar Energy in remote placesplaces

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Electromagnetic InductionElectromagnetic Induction

N

The direction of the induced current is reversed if…

1) The wire is moved in the opposite direction

2) The field is reversed

The size of the induced current can be increased by:

1) Increasing the speed of movement

2) Increasing the magnet strength

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ElectromagnetElectromagnetic inductionic induction

The direction of the induced current is reversed if…

1) The magnet is moved in the opposite direction

2) The other pole is inserted first

The size of the induced current can be increased by:

1) Increasing the speed of movement

2) Increasing the magnet strength

3) Increasing the number of turns on the coil

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AC GeneratorsAC Generators

SN

Voltage

Time

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Other generatorsOther generatorsA dynamo works by the same principle.

1) How can you make its output bigger?

2) How can you reverse the direction of its output current?

Large-scale production of Large-scale production of ElectricityElectricity

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A generator at Drax power station in England

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DC and ACDC and AC

DC stands for “Direct Current” – the current only flows in one direction:

AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz)

1/50th s

230V

V

V

Time

T

19/04/23The National GridThe National GridElectricity reaches our homes from power stations through the National Grid:

If electricity companies transmitted electricity at 240 volts through overhead power lines there would be too much ______ loss by the time electricity reaches our homes. This is because the current is ___. To overcome this they use devices called transformers to “step up” the voltage onto the power lines. They then “____ ____” the voltage at the end of the power lines before it reaches our homes. This way the voltage is _____ and the current and power loss are both ____.

Words – step down, high, power, low, high

Power stationStep up

transformerStep down

transformerHomes

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Power LinesPower Lines

Here’s my new shed. I want to connect it to the electricity I my

house. Should I use an overhead cable or bury

the cable underground?

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TransformersTransformers

Transformers are used to _____ __ or step down _______. They only work on AC because an ________ current in the primary coil causes a constantly alternating _______ ______. This will “_____” an alternating current in the secondary coil.

Words – alternating, magnetic field, induce, step up, voltage

We can work out how much a transformer will step up or step down a voltage:

Voltage across primary (Vp)

No. of turns on secondary (Ns)

Voltage across secondary (Vs)

No. of turns on primary (Np)

19/04/23Some transformer Some transformer questionsquestions

Primary voltage

Vp

Secondary voltage

Vs

No. of turns on

primary Np

No. of turns on

secondary Ns

Step up or step down?

12V 24V 100 ? ?

400V 200V 20 ? ?

25,000V 50,000V 1,000 ? ?

23V 230V 150 ? ?

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Some example questionsSome example questionsPrimary voltage

Vp

Secondary voltage

Vs

No. of turns on

primary Np

No. of turns on

secondary Ns

Step up or step down?

6V 24V 100 ? ?

400,000V 200V ? 1,000 ?

25,000V ? 20,000 20 ?

? 230V 150 1,500 ?

1) A transformer increases voltage from 10V to 30V. What is the ratio of the number of turns on the primary coil to the number of turns on the secondary coil?

2) A step-down transformer has twice as many turns on the primary coil than on the secondary coil. What will be the output (secondary) voltage if the input voltage is 50V?

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The Cost of ElectricityThe Cost of ElectricityElectricity is measured in units called “kilowatt hours” (kWh). For example…

A 3kW fire left on for 1 hour uses 3kWh of energy

A 1kW toaster left on for 2 hours uses 2kWh

A 0.5kW hoover left on for 4 hours uses __kWh

A 200W TV left on for 5 hours uses __kWh

A 2kW kettle left on for 15 minutes uses __kWh

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The Cost of ElectricityThe Cost of ElectricityTo work out how much a device costs we do the following:

Cost of electricity = Power (kW) x time (h) x cost per kWh (p)

For example, if electricity costs 8p per unit calculate the cost of the following…

1) A 2kW fire left on for 3 hours

2) A 0.2kW TV left on for 5 hours

3) A 0.1kW light bulb left on for 10 hours

4) A 0.5kW hoover left on for 1 hour

48p

8p

8p

4p

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Reducing Energy ConsumptionReducing Energy Consumption

25W “energy efficient” light bulb, £7.30 on Amazon

60W older bulb, roughly 70p, to be banned in the EU

from 2012.

1) Which one is more cost-effective?

2) Jane wants to replace all the bulbs in her house with energy-efficient ones. If she has 10 light bulbs in her house calculate the following:

a) How much will it cost her to buy the bulbs?

b) What will the total power consumption be reduced by?

c) If she uses the bulbs for 5 hours per day and electricity costs 10p per unit how much money will she save?

d) How long will it take her to repay the cost of the bulbs?

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Energy 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)

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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?

Topic 6 – Energy and the Topic 6 – Energy and the FutureFuture

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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

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The Laws of PhysicsThe Laws of PhysicsThere 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

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Energy changesEnergy changesTo 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

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Conservation of EnergyConservation of EnergyIn 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

19/04/23EfficiencyEfficiencyEfficiency 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)

Light (80J)

Sound (40J)

Heat (?)

Efficiency = Useful energy out

Energy in

x100%

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Some examples of efficiency…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?

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

19/04/23Energy Transfer (“Sankey”) Energy Transfer (“Sankey”) diagramsdiagrams

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

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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?

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RadiationRadiationAn introduction…

I’m very hot!I’m cool!

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Some examples of radiationSome examples of radiation

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Some examples of radiationSome examples of radiation

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Heat Loss from a HouseHeat Loss from a House

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Radiation PracticalRadiation PracticalTime / min Temperature in each container / 0C

Black Silver Clear

1

2

3

4

5

6

7

8

9

10

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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 __________. Dark, matt colours will absorb AND emit the _____ infra-red radiation, and light, shiny colours will ________ it.

For a body to stay at constant temperature it must radiate the same average ______ that it absorbs.

RadiationRadiation

Words – reflect, infra-red, waves, most, power