Energy for the Home

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Energy for the Home
(OCR)
W Richards The Weald School
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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 giving out, warm up, taking in, cool down
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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 its fairly clear that
the amount of energy it gains depends on how much
water there is and how hot it gets
Energy a mass x temperature rise
Energy mass x s.h.c x temp
E mc?T
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Specific Heat Capacity
How can we do this experimentally?
E VIt and E mc?T
Possible errors with this experiment

• Temperature throughout the liquid should be the
  same
• Solution

• Heat is lost to the surroundings
• Solution(s)

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Heating ice
Temp/OC
150
100
50
0
-50




Time/s
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Latent Heat of Fusion
From the previous slide we can say that the
energy needed to melt water is given by
Energy mass x specific latent heat of fusion
To work out L experimentally you could
VIt mL
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House insulation
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House insulation
Type of insulation Cost Annual amount saved
Loft insulation 400 80
Double Glazing 2,000 50
Cavity wall ins. 600 60
Draught excluder 40 20

1. Which type of insulation costs the most?
2. Which type of insulation is the most effective?
3. Which type is the most cost effective?
4. Which type pays for itself after 40 years?

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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
Light (80J)
Electrical Energy (200J)
Sound (40J)
Heat (?)
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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?
3. A steam engine is 50 efficient. If it delivers
   20,000J of movement energy how much chemical
   energy was put into it?

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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.
Heating a non-metal
Heating a metal
Words vibrations, electrons, solid, heated,
better
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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
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Some questions on 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.

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Radiation
An introduction
Im cool!
Im very hot!
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Some examples of radiation
Thermograms
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Some examples of radiation
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Radiation Practical
Time / min Temperature in each container / 0C Temperature in each container / 0C Temperature in each container / 0C
Time / min Black Silver Clear
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2
3
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8
9
10
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Radiation
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 wouldnt 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
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Understanding Heat Transfer
1) Explain how and where all 3 processes of heat
transfer happen in a bonfire
2) By considering how a Thermos Flask is built
explain how it manages to keep hot drinks hot and
cold drinks cold.
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Understanding Heat Transfer 2
3) Car radiators are designed to help car
engines lose heat. Explain how they do this.
4) Some houses have solar collectors on their
roof. Explain how they work
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Electromagnetic Radiation
E-M radiation is basically a movement of energy
in the form of a wave. Some examples
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The Electromagnetic Spectrum
Each type of radiation shown in the
electromagnetic spectrum has a different
wavelength and a different frequency
Gamma rays X-rays Ultra violet Visible light Infra red Microwaves Radio/TV
Each of these types travels at the same speed
through a _______ (300,000,000m/s), and different
wavelengths are absorbed by different surfaces
(e.g. infra red is absorbed very well by
___________ surfaces). This absorption may heat
the material up (like infra red and _______) or
cause an alternating current (like in a __
_______).
Words black, microwaves, long, short, TV
aerial, vacuum
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The Electromagnetic Spectrum
Type of radiation
Uses
Dangers
Treating cancer, sterilisation
Gamma rays
Cell mutation
X rays
Medical
Cell mutation
UVA, UVB and UVC
Sun beds
Skin cancer
None (unless you look at the sun)
Visible light
Seeing things
Remote controls, heat transfer
Infra red
Sunburn
Microwaves
Satellites, phones
Burns
TV/radio
Communications
Very few
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Refraction through a glass block
Wave slows down but is not bent, due to entering
along the normal
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(No Transcript)
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Refraction
Refraction is when waves ____ __ or slow down due
to travelling in a different _________. A medium
is something that waves will travel through.
When a pen is placed in water it looks like
this In this case the light rays are slowed
down by the water and are _____, causing the pen
to look odd. The two mediums in this example are
______ and _______.
Words speed up, water, air, bent, medium
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Finding the Critical Angle
1) Ray gets refracted
2) Ray still gets refracted
4) Ray gets internally reflected
3) Ray still gets refracted (just!)
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Uses of Total Internal Reflection
Optical fibres An optical fibre is a long,
thin, _______ rod made of glass or plastic.
Light is _______ reflected from one end to the
other, making it possible to send ____ chunks of
information
Optical fibres can be used for _________ by
sending electrical signals through the cable.
The main advantage of this is a reduced ______
loss.
Words communications, internally, large,
transparent, signal
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Analogue vs. Digital
Analogue signals (like talking or music)
continually vary in amplitude and/or frequency
Digital signals, however, are either off or on,
and the information is sent in a series of pulses

• There are two main advantages of digital
• More information can be sent down the same cable
• Better quality, because a digital signal can be
  amplified without amplifying the extra noise

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Wireless devices
The trouble with optical fibres and electrical
connections is that they need wires. This is a
big advantage with sending information using
radio waves and microwaves. However, they have
disadvantages as well...
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Blocking reception
Microwaves can be blocked by obstructions
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Using Satellites with microwaves
Microwaves are used to communicate with satellites
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Using Radio waves
Radio waves are reflected off the ionosphere (an
electrically charged layer in the atmosphere)
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Diffracting Radio Waves
A low frequency radio wave can be diffracted over
obstacles but some signal strength will be lost.
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Some definitions
1) Amplitude this is how high the wave is
2) Wavelength (?) this is the distance between
two corresponding points on the wave and is
measured in metres
3) Frequency this is how many waves pass by
every second and is measured in Hertz (Hz)
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Some definitions
Transverse waves are when the displacement is at
right angles to the direction of the wave
Longitudinal waves are when the displacement is
parallel to the direction of the wave
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The Wave Equation
The wave equation relates the speed of the wave
to its frequency and wavelength
Wave speed (v) frequency (f) x wavelength
(?) in m/s in Hz
in m
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Some example wave equation questions

1. A water wave has a frequency of 2Hz and a
   wavelength of 0.3m. How fast is it moving?
2. A water wave travels through a pond with a speed
   of 1m/s and a frequency of 5Hz. What is the
   wavelength of the waves?
3. The speed of sound is 330m/s (in air). When Dave
   hears this sound his ear vibrates 660 times a
   second. What was the wavelength of the sound?
4. Purple light has a wavelength of around 6x10-7m
   and a frequency of 5x1014Hz. What is the speed
   of purple light?

0.6m/s
0.2m
0.5m
3x108m/s
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Lasers
Lasers produce light waves that are coherent
i.e. they have the same frequency and they are in
phase
These two waves have different amplitudes but the
same frequency and hit their peaks at the same
time they are in phase
These two waves start opposite to each other
they are in antiphase
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Using lasers in CDs
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The Structure of the Earth
How do we know this? These facts have all been
discovered by examining seismic waves
(earthquakes)
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Seismic waves
Earthquakes travel as waves through the Earth
we call them SEISMIC WAVES. There are two types

• P waves
• They are longitudinal so they cause the ground to
  move up and down
• They can pass through solids and liquids
• They go faster through more dense material

• S waves
• They are transverse so they cause the ground to
  move from right to left
• They ONLY pass through solids
• They are slower than P waves
• They go faster through more dense material

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Seismic waves
The paths of these waves are all curved because
density is gradually changing
These observations tell us 3 things about the
Earth 1) It has a thin crust, 2) it has a
semi-fluid mantle where density increases with
depth, 3) a core with a liquid outer part and a
solid inner part.
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Suncream
Ultra violet radiation in sunshine can be
dangerous and cause skin cancer
Safe time exposure time (e.g. 20 mins) x sun
block factor
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Global Warming

• Facts
• The 10 warmest years of the last century have all
  occurred within the last 15 years
• Sea level has risen by between 12 and 24cm in the
  last 100 years
• Rainfall has risen by 1

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Ozone