Transcript Using Waves

EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 3-2
Using Waves
(The Electromagnetic Spectrum)
Edexcel IGCSE Physics pages 99 to 106
Content applying to Triple Science only is shown in
red type on the next slide and is indicated on
subsequent slides by ‘TRIPLE ONLY’
June 17th 2012
Edexcel Specification
Section 3: Waves
c) The electromagnetic spectrum
understand that light is part of a continuous electromagnetic spectrum which includes radio, microwave, infrared, visible, ultraviolet, x-ray and
gamma ray radiations and that all these waves travel at the same speed in free space
identify the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours of the
visible spectrum
explain some of the uses of electromagnetic radiations, including:
• radio waves: broadcasting and communications
• microwaves: cooking and satellite transmissions
• infrared: heaters and night vision equipment
• visible light: optical fibres and photography
• ultraviolet: fluorescent lamps
• x-rays: observing the internal structure of objects and materials and medical applications
• gamma rays: sterilising food and medical equipment
understand the detrimental effects of excessive exposure of the human body to electromagnetic waves, including:
• microwaves: internal heating of body tissue
• infra-red: skin burns
• ultraviolet: damage to surface cells and blindness
• gamma rays: cancer, mutation.
and describe simple protective measures against the risks.
d) Light and sound
understand the difference between analogue and digital signals
describe the advantages of using digital signals rather than analogue signals
describe how digital signals can carry more information
Red type: Triple Science Only
The Electromagnetic Spectrum
The electromagnetic spectrum is a continous
spectrum of waves which includes the visible
spectrum.
The electromagnetic spectrum is divided into
seven bands which in order of decreasing
wavelength are:
RADIO WAVES
LONGEST
WAVELENGTH
MICROWAVES
INFRA-RED
VISIBLE LIGHT
ULTRA-VIOLET
X-RAYS
GAMMA RAYS
SHORTEST
WAVELENGTH
Listing in order of decreasing frequency
and energy:
GAMMA RAYS
HIGHEST
FREQUENCY
GREATEST
ENERGY
LOWEST
FREQUENCY
LEAST
ENERGY
X-RAYS
ULTRA-VIOLET
VISIBLE LIGHT
INFRA-RED
MICROWAVES
RADIO WAVES
Common properties
All electromagnetic waves, including visible light have the
following common properties:
1. They transfer energy
2. They are all transverse waves
3. They all travel at the same speed through
a vacuum (300 000 000 m/s)
4. They can all be reflected, refracted and diffracted**
Notes:
(a) 300 000 00 m/s is the same as 186 000 miles per second.
(b) Through air, light and the other waves travel at about the above speed
but through denser substances (for example glass) the speed falls.
(c) According to Albert Einstein’s Theory of Relativity nothing can travel
faster than the speed of light through a vacuum.
(d) ** Double Science students do not need to know about diffraction
Question 1
Calculate the wavelength of a radio wave in of frequency
100 MHz if its speed is 300 000 000 m/s.
wave speed (v) = frequency (f) x wavelength (λ)
becomes:
λ=v÷f
= 300 000 000 m/s ÷ 100 MHz
= 300 000 000 m/s ÷ 100 000 000 Hz
wavelength = 3.0 metres
Question 2
Calculate the frequency of a light wave of wavelength 0.000
7mm of speed 300 000 000 m/s.
v=fxλ
becomes:
f=v÷λ
= 300 000 000 m/s ÷ 0 000 7 mm
= 300 000 000 m/s ÷ 0 000 000 7 m
frequency = 429 000 000 000 000 Hz
(or = 4.29 x 1014 Hz)
Answers
Complete:
highest
frequency
longest
wavelength
greatest
energy
GAMMA
RADIO
GAMMA
X-RAYS
MICROWAVES
X-RAYS
ULTRAVIOLET
INFRA-RED
ULTRAVIOLET
VISIBLE LIGHT
VISIBLE LIGHT
VISIBLE LIGHT
INFRA-RED
ULTRAVIOLET
INFRA-RED
MICROWAVES
X-RAYS
MICROWAVES
RADIO
GAMMA
RADIO
lowest
frequency
shortest
wavelength
least
energy
Choose appropriate words to fill in the gaps below:
spectrum
The electromagnetic __________
is a group of waves that are
seven
divided into ________
bands.
shortest wavelength, highest
Gamma rays have the ________
energy
frequency and ________.
The rest of the spectrum, in order
of increasing wavelength are:
x-rays, _________,
ultraviolet visible light, infra-red, ___________
microwaves and
radio waves.
speed
All electromagnetic waves travel at the same _______
vacuum
through a __________,
300 000 000 m/s.
WORD SELECTION:
shortest energy spectrum vacuum ultraviolet
speed seven microwaves
Radio waves
Radio and television both use radio waves
RADIO
MICROWAVES
INFRA-RED
LIGHT
ULTRA-VIOLET
X-RAYS
GAMMA RAYS
Radio waves have the longest
wavelengths of the
electromagnetic spectrum,
typically 100 metres.
A radio
transmitter
Uses of radio waves
Radio waves are
used in:
• radio and television
communication
• medicine with MRI
scanners
• astronomy to ‘see’
the centre of our
galaxy
MRI scanner and scan
Radio telescope
Transmitting and receiving radio waves
Radio waves are emitted from a transmitter aerial when
an alternating voltage is connected to the aerial. The
radio wave emitted has the same frequency as the
alternating voltage.
When these radio waves pass across a receiver aerial,
they cause a tiny alternating voltage of the same
frequency to occur in the aerial.
radio wave
transmitter
receiver
TRIPLE ONLY
Diffraction
Diffraction occurs when a
wave spreads out from a gap
or bends around an obstacle.
Diffraction is more significant
with low frequency, long
wavelength waves.
Diffraction out of a gap
Diffraction results in the energy
of the wave spreading out.
Diffraction around
an obstacle
Radio frequency bands
The radio and microwave part of the electromagnetic spectrum is subdivided into frequency bands. The uses of each band depends on its
frequency range.
The higher the frequency:
• The more information that can be carried – this can result in
better quality sound and video or more channels.
• The shorter their range – due to greater absorption by the
atmosphere.
• The less the signal spreads out – less diffraction – hills and
large buildings also are more likely to stop the signal.
Higher frequency
waves are less able
to diffract around
buildings and hills
Wavebands
Waveband
Microwaves
Frequency range
greater than 3 GHz
(wavelength less than 10 cm)
UHF (ultra-high frequency)
300 MHz – 3 GHz
(wavelengths: 10 - 100 cm)
VHF (very-high frequency)
30 MHz – 300 MHz
(wavelengths: 1 - 10 m)
Uses
Satellite TV
Mobile phones
Terrestrial TV
Mobile phones
FM radio
Emergency services
Digital radio
HF (high frequency)
3 MHz – 30 MHz
also called ‘short wave’ or SW
(wavelengths: 10 – 100 m)
Amateur radio
International radio (AM)
MF (medium frequency)
300 kHz – 3 MHz
National radio (AM)
also called ‘medium wave’ or MW
(wavelengths: 100 – 1000 m)
LF (low frequency)
30 kHz – 300 MHz
also called ‘long wave’ or LW
(wavelengths: 1 – 10 km)
VLF (very-low frequency)
less than 30 kHz
(wavelengths more than 10 km)
International radio (AM)
Submarine
communication
Note: 1 GHz = 1000 MHz; 1 MHz = 1000 kHz; 1 kHz = 1000 Hz
Radio waves and the ionosphere
The ionosphere is a layer of gas in
the upper atmosphere that reflects
radio waves of frequencies less
than about 30 MHz.
The ionosphere is stronger in
summer than winter and so distant
radio stations can be received
better in summer.
Radio waves can be reflected off
the bottom of the ionosphere
enabling them to travel great
distances.
Before the advent of satellites,
using the ionosphere was one of
the main ways of communicating
around the world.
Microwaves
Two uses of microwaves
RADIO
MICROWAVES
INFRA-RED
LIGHT
ULTRA-VIOLET
X-RAYS
GAMMA RAYS
Microwaves have wavelengths
of typically 10 cm.
Microwave
transmitter / receiver
used for a mobile
phone network.
Uses of microwaves
Microwaves are used for:
• cooking
• mobile phone
communication
• satellite television
• astronomy – finding
out about the origin of
the Universe
Satellite
television
receiver
Cosmic Microwave Background Radiation
Dangers of microwaves
Microwaves can cause
internal heating of body
tissue.
Microwave ovens contain
metal shielding to prevent the
microwaves from leaking out.
Some people believe that over
use of mobile phones can
lead to brain damage.
Infra-red radiation
An infra-red or
thermal image.
RED = hot
BLUE = cold
Despite appearances this
heater is giving off mostly
invisible infra-red radiation.
RADIO
MICROWAVES
INFRA-RED
LIGHT
ULTRA-VIOLET
X-RAYS
Infra-red waves have
wavelengths of typically a
millionth of a metre (1
micrometre)
They are emitted by all objects.
The hotter the object, the more
infra-red radiation is emitted.
GAMMA RAYS
Infra-red
photograph.
brighter = hotter
Uses of infra-red
Infra-red waves are used:
• to cook food
• by remote controls
• in communication
systems using optical
fibres
• to detect intruders in
burglar alarms
• in ‘night sights’
• in astronomy to see
behind gas clouds
Choose appropriate words to fill in the gaps below:
longer
Infra-red radiation has a _________
wavelength than visible
emitted by all objects. The higher the
light and is _________
temperature of an object the greater is the amount of IR
___________
radiation emitted.
centimetres
Microwaves have wavelengths of a few ___________
and are
cooking and communication.
used for ________
lowest
Radio waves have the longest wavelengths but the ________
frequencies of the electromagnetic spectrum. Radio waves
galaxy
are used to study the centre of our _________.
WORD SELECTION:
emitted lowest
galaxy
cooking temperature longer centimetres
Visible light
RADIO
RED
MICROWAVES
ORANGE
INFRA-RED
YELLOW
LIGHT
GREEN
ULTRA-VIOLET
BLUE
X-RAYS
INDIGO
GAMMA RAYS
VIOLET
Visible light is emitted
from hot objects like the
Sun.
Visible light has
wavelengths ranging
from:
0.000 000 4m (violet)
to
0.000 000 7m (red).
White light can be
split into the
colour spectrum
using a prism or
with water.
Uses of visible light
Visible light is used:
• for sight
• in photography
• in optical fibres
• in photosynthesis
Ultraviolet
Security markings show
up under ultraviolet light
Ultraviolet emitted
by the Sun
Fluorescent lamps
and energy efficient
bulbs work using uv
RADIO
MICROWAVES
INFRA-RED
LIGHT
Ultraviolet has a wavelength of
typically of a ten millionth of a
metre.
UV is produced from very hot
objects like the Sun or from special
electrical tubes.
ULTRA-VIOLET
X-RAYS
GAMMA RAYS
Most of the Sun’s ultraviolet
radiation is absorbed by the Ozone
layer in the upper part of the Earth’s
atmosphere.
UV is also stopped by glass.
Uses of ultraviolet
Ultraviolet is used in:
• Fluorescent lamps
including energy
efficient light bulbs
• Security devices
• Dentistry
• Pest control
• Astronomy
A bird appears on many
Visa credit cards when held
under a UV light source
Ultraviolet light used in
cosmetic dentistry
‘zapper’ attracts
insects using uv
Safety with ultraviolet
The Sun’s ultraviolet light is
responsible for sun tan.
Too much exposure to UV can
cause blindness and skin cancer.
2
4
sunglasses
with UV
protection
1
wear
a hat
3
cover up
when the
Sun is
strongest
longer
shorts offer
protection
5
use a high sun protection
factor sunscreen – reapply
after swimming
X-rays
X-ray photographs
Exploding stars
emit X-rays
RADIO
X-rays have wavelengths of typically
a billionth of a metre.
MICROWAVES
INFRA-RED
LIGHT
They are produced from X-ray tubes
that use very high voltage (typically
one hundred thousand volts).
ULTRA-VIOLET
X-RAYS
GAMMA RAYS
They are very penetrating and are
only stopped by several centimetres
of lead.
Uses of X-rays
X-rays are used in:
• X-ray photographs
• Airport security
• Cancer treatment
• Astronomy
Taking an X-ray (radiograph)
X-rays pass through soft
tissue but are absorbed by
bones.
X-rays are directed onto the
patient from the X-ray tube.
A light proof cassette
containing a photographic
film is placed on the other
side of the patient.
A patient being prepared
for a radiograph
When the X-ray tube is switched
on, the X-rays pass through the
patient’s body leaving a
‘shadow’ image on the film
showing the bones.
When the film is developed the
parts exposed by the X-rays are
darker than the other parts.
The bones show up as lighter
regions on the radiograph.
A chest X-ray
Gamma Rays
Gamma rays are
given off by nuclear
explosions
Gamma rays are emitted
from material falling into
black holes
Gamma Rays
RADIO
MICROWAVES
INFRA-RED
Gamma rays have the shortest
wavelengths of the
electromagnetic spectrum,
typically a millionth millionth of a
metre.
LIGHT
ULTRA-VIOLET
They are emitted by radioactive
substances.
X-RAYS
GAMMA RAYS
They are very penetrating and are
only stopped by several
centimetres of lead.
Uses of gamma rays
Gamma rays are used:
• to kill cancer cells
• to kill harmful
bacteria in food
• to sterilise surgical
instruments
Gamma rays being used
to treat cancer
Safety with gamma and X-rays
Too much exposure to gamma rays
or X-rays is dangerous.
High doses kill living cells. Low
doses cause cell mutation and
cancerous growth.
Workers who use equipment
producing gamma or X-rays wear a
film badge called a dosemeter. The
film in the badge darkens if the
person receives a too high dosage
of radiation.
a dosemeter
Choose appropriate words to fill in the gaps below:
dangerous radiations of the
Gamma and X-rays are the most _________
mutation
electromagnetic spectrum. Both can cause cell _________
and cancerous growth although both can also be used to
cancer
treat ________.
lead to be stopped.
Both require several centimetres of ______
bones allowing the production of
X-rays are absorbed by ______
radiographs.
bacteria in food and to
Gamma rays are used to kill _________
sterilise
_________
medical instruments.
WORD SELECTION:
bones mutation cancer bacteria lead dangerous sterilise
TRIPLE ONLY
Communication With Waves
TRIPLE ONLY
Analogue and digital signals
Communication signals may be
analogue or digital.
Analogue signals vary
continuously in amplitude
between zero and some
maximum level.
Digital signals only have two
voltage levels, for example +5V
and 0V.
TRIPLE ONLY
Examples of analogue and digital systems
ANALOGUE
DIGITAL
TRIPLE ONLY
Advantages of using digital signals
1. Less interference than with analogue signals.
Interference causes a hissing noise with analogue radio.
This does not happen with digital signals because
regenerator circuits are used to clean ‘noisy’ pulses. So a
digital signal has a higher quality than an analogue one.
Regenerator
‘Noisy’ pulse in
‘Clean’ pulse out
TRIPLE ONLY
2. Much more information can be sent.
Digital pulses can be made very short so more pulses can be
carried each second. Different signals can be sent together by
a process called multiplexing.
3. Digital signals are easily processed by computers.
Computers are digital devices!
Online Simulations
Sequential Puzzle on EM Spectrum Wavelength order- by
KT - Microsoft WORD
Sequential Puzzle on EM Spectrum Frequency order- by KT
- Microsoft WORD
Hidden Pairs Game on EM Spectrum Uses - by KT Microsoft WORD
Electromagnetic Spectrum bounce quiz - eChalk
Radio Waves & Electromagnetic Fields - PhET - Broadcast
radio waves from KPhET. Wiggle the transmitter electron
manually or have it oscillate automatically. Display the field
as a curve or vectors. The strip chart shows the electron
positions at the transmitter and at the receiver.
Microwaves - PhET - How do microwaves heat up your
coffee? Adjust the frequency and amplitude of microwaves.
Watch water molecules rotating and bouncing around. View
the microwave field as a wave, a single line of vectors, or
the entire field.
Thermal Camera Pictures - falstad
The Greenhouse Effect - PhET - Just how do greenhouse
gases change the climate? Select the level of atmospheric
greenhouse gases during an ice age, in the year 1750,
today, or some time in the future and see how the Earth's
temperature changes. Add clouds or panes of glass.
Making X-rays - Colorado
X-rays - Fluoroscope demo - Colorado
Fibre optic reflection - NTNU
BBC AQA GCSE Bitesize Revision:
What is a spectrum
The electromagnetic spectrum - table
Radio waves
Microwaves
UV & IR
Gamma & X-rays
Hazards of radiation
Optical fibres
Analogue & digital signals
Comaparing analogue & digital
TRIPLE ONLY
Using Waves
Notes questions from pages 99 to 106
1.
2.
3.
4.
5.
6.
7.
Copy the table on page 106.
Give five common properties of all members of the electromagnetic
spectrum. (see page 99)
List the colours of the visible spectrum in order of increasing
wavelength. (see page 102)
State the hazards of (a) microwaves; (b) ultra-violet; (c) X-rays and
gamma rays. (see pages 101 to 103)
(a) Explain the difference between analogue and digital signals. (b)
What are the advantages of using digital signals? (see pages 104
and 105)
Answer the questions on page 106.
Verify that you can do all of the items listed in the end of chapter
checklist on page 106.
DOUBLE SCIENCE ONLY
Using Waves
Notes questions from pages 99 to 106
1. Copy the table on page 106.
2. Give five common properties of all members of
the electromagnetic spectrum. (see page 99)
3. List the colours of the visible spectrum in order
of increasing wavelength. (see page 102)
4. State the hazards of (a) microwaves; (b) ultraviolet; (c) X-rays and gamma rays. (see pages
101 to 103)
5. Answer questions 1 and 2 on page 106.