AQA GCSE 1b-5a Electromagnetic Waves Part A

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AQA GCSE 1b-5aElectromagnetic WavesPart A
General, Gamma, X-rays, UV Light

• AQA GCSE Physics pages 78 to 83
• AQA GCSE Science pages 282 to 287

September 20th 2010
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AQA GCSE Specification

• THE ELECTROMAGNETIC SPECTRUM
• 11.5 What are the uses and hazards of the waves
  that form the electromagnetic spectrum?
• Using skills, knowledge and understanding of how
  science works
• to evaluate the possible hazards associated
  with the use of different types of
  electromagnetic radiation
• to evaluate methods to reduce exposure to
  different types of electromagnetic radiation.
• Skills, knowledge and understanding of how
  science works set in the context of
• Electromagnetic radiation travels as waves and
  moves energy from one place to another.
• All types of electromagnetic waves travel at
  the same speed through a vacuum (space).
• The electromagnetic spectrum is continuous but
  the wavelengths within it can be grouped into
  types of increasing wavelength and decreasing
  frequency gamma rays, X-rays, ultraviolet
  rays, visible light, infra red rays, microwaves
  and radio waves.
• Different wavelengths of electromagnetic
  radiation are reflected, absorbed or transmitted
  differently by different substances and types of
  surface.
• Different wavelengths of electromagnetic
  radiation have different effects on living cells.
  Some radiations mostly pass through soft tissue
  without being absorbed, some produce heat, some
  may cause cancerous changes and some may kill
  cells. These effects depend on the type of
  radiation and the size of the dose.
• The uses and the hazards associated with the
  use of each type of radiation in the
  electromagnetic spectrum.
• Electromagnetic waves obey the wave formula
• wave speed frequency wavelength

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Waves

• A wave is a means of transferring energy from one
  point to another without there being any transfer
  of any substance between the two points.

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Wavelength

• Wavelength is the distance between one wave peak
  and the next wave peak along the path of a wave.
• Wavelength is measured in metres

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Frequency

• Frequency is the number of wave peaks that pass a
  point in one second.
• Frequency is measured in hertz (Hz)
• 1 Hz 1 peak per second
• 2 Hz 2 peaks per second and so on.
• 1 kilohertz (1kHz) 1 000 Hz
• 1 megahertz (1MHz) 1 000 000 Hz
• 1 gigahertz (1GHz) 1 000 000 000 Hz
• 1 terahertz (1THz) 1 000 000 000 000 Hz

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The wave equation

• speed frequency x wavelength
• speed in metres per second (m/s)
• wavelength in metres
• frequency in hertz
• Also
• frequency speed wavelength
• and
• wavelength speed frequency

speed
wavelength
frequency
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Question 1

• Calculate the speed of a water wave of wavelength
  3m and frequency 6Hz.
• speed frequency x wavelength
• 6Hz x 3m
• speed 18 m/s

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Question 2

• Calculate the wavelength of a sound wave in water
  of frequency 300Hz if its speed is 1500m/s.
• speed frequency x wavelength
• becomes
• wavelength speed frequency
• 1500 m/s 300 Hz
• wavelength 5 metres

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Complete
Answers
speed frequency wavelength
15 Hz 4 m
330 m/s 2 m
300 000 000 m/s 1 500 m
300 000 km/s 100 MHz
60 m/s
165 Hz
200 000 Hz
3 m
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The Electromagnetic Spectrum

• These are a group of waves that consist of
  electric and magnetic disturbances that transfer
  energy from one place to another.

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• The properties and energy transferred by these
  waves depends on their wavelengths.

LONGEST WAVELENGTH
RADIO WAVES
MICROWAVES
INFRA-RED
VISIBLE LIGHT
ULTRA-VIOLET
X-RAYS
GAMMA RAYS
SHORTEST WAVELENGTH
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• Their energies and frequencies are proportional

HIGHEST ENERGY AND FREQUENCY
GAMMA RAYS
X-RAYS
ULTRA-VIOLET
VISIBLE LIGHT
INFRA-RED
MICROWAVES
LOWEST ENERGY AND FREQUENCY
RADIO WAVES
Note that the energy and frequency order is the
reverse of the wavelength order.
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The electromagnetic spectrum
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The speed of light

• All electromagnetic waves, including visible
  light, travel at the same speed through a vacuum.
• This is 300 000 000 metres per second (m/s)
• or 300 000 kilometres per second (km/s) or 186
  000 miles per second
• Notes
• Through air, light and the other waves travel at
  about the above speed.
• Through denser substances (for example glass) the
  speed falls.
• According to Albert Einsteins Theory of
  Relativity nothing can travel faster than the
  speed of light through a vacuum.

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Complete
Answers
highest frequency
longest wavelength
greatest energy
GAMMA
RADIO
GAMMA
X-RAYS
MICROWAVES
X-RAYS
ULTRAVIOLET
ULTRAVIOLET
INFRA-RED
VISIBLE LIGHT
VISIBLE LIGHT
VISIBLE LIGHT
INFRA-RED
ULTRAVIOLET
INFRA-RED
MICROWAVES
X-RAYS
MICROWAVES
RADIO
GAMMA
RADIO
lowest frequency
shortest wavelength
least energy
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Choose appropriate words to fill in the gaps
below The electromagnetic __________ is a group
of waves that vary in their properties with their
____________. Gamma rays have the ________
wavelength, highest frequency and ________. The
rest of the group, in order of increasing
wavelength are x-rays, _________, visible light,
infra-red, ___________ and radio waves. All
electromagnetic waves travel at the same _______
through a __________, 300 000 000 m/s.
spectrum
wavelengths
shortest
energy
ultraviolet
microwaves
speed
vacuum
WORD SELECTION
vacuum
shortest
ultraviolet
energy
spectrum
wavelengths
microwaves
speed
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Simulations

• Electromagnetic Wave - Fendt
• Electromagnetic wave - NTNU
• Hidden Pairs Game on EM Spectrum Frequencies - by
  KT - Microsoft WORD
• Hidden Pairs Game on EM Spectrum Wavelengths - by
  KT - Microsoft WORD
• Sequential Puzzle on EM Spectrum Wavelength
  order- by KT - Microsoft WORD
• Sequential Puzzle on EM Spectrum Frequency order-
  by KT - Microsoft WORD
• Fifty-Fifty Game on EM Spectrum Frequency - by KT
  - Microsoft WORD
• Fifty-Fifty Game on EM Spectrum Wavelength - by
  KT - Microsoft WORD
• Hidden Pairs Game on EM Spectrum Uses - by KT -
  Microsoft WORD
• Electromagnetic Spectrum bounce quiz - eChalk

• BBC Bitesize Revision
• Introduction Page to AQA Electromagnetic Spectrum
  
• What is a spectrum? - shows prism dispersing
  light
• The Electromagnetic Spectrum - Summary Table
• Test bite on the Electromagnetic Spectrum

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The electromagnetic spectrumNotes questions from
pages 78/282 79/283

1. What are electromagnetic waves?
2. Sketch a copy of Figure 1 on page 78/282 but
   without the photographs of the various devices.
3. What is meant by (a) wavelength and (b)
   frequency? Illustrate your answer to (a) with a
   diagram.
4. Copy and answer questions (a) and (b) on page
   78/282.
5. How fast do electromagnetic waves travel through
   a vacuum?
6. Copy the equation for wave speed, along with the
   units used, at the top of page 79/283.
7. Copy and answer questions (c) and (d) on page
   79/283.
8. Copy the Key Points on page 79/283.
9. Answer the summary questions on page 79/283.

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The electromagnetic spectrum ANSWERS

• In text questions
• Ultraviolet
• Microwaves
• 2.94 m
• 200 000 Hz
• (or 200 kHz)

• Summary questions
• (a) Smaller than
• (b) The same as
• (c) Greater than
• 2. (a) Microwaves, ultraviolet, gamma rays.
• (b) (i) 0.5 m
• (ii) 1000 MHz

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Gamma Rays
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Gamma Rays

• Gamma rays have the shortest wavelengths of the
  electromagnetic spectrum, typically 1 picometre.
• (0.000 000 000 001 m, a millionth millionth of a
  metre).
• They are emitted by radioactive substances.
• They are very penetrating and are only stopped by
  several centimetres of lead.

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Uses of gamma rays

• Gamma rays are used
• to kill harmful bacteria in food
• to sterilise surgical instruments
• to kill cancer cells

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X-rays
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X-rays

• X-rays have wavelengths of typically 1
  nanometre.
• (0.000 000 001 m, a billionth of a metre).
• They are produced from X-ray tubes that use very
  high voltages (100 000V plus)
• They are very penetrating and are only stopped by
  several centimetres of lead.

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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.

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• When the X-ray tube is switched on, the X-rays
  pass through the patients 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.

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Airport security cameras

• These also use X-rays with special cameras.
• Metallic objects, for example guns, absorb X-rays
  in the same way as bones.

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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.

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Choose appropriate words to fill in the gaps
below Gamma and X-rays are the most _________
radiations of the electromagnetic spectrum. Both
can cause cell _________ and cancerous growth
although both can also be used to treat
________. Both require several centimetres of
______ to be stopped. X-rays are absorbed by
______ allowing the production of
radiographs. Gamma rays are used to kill
_________ in food and to _________ medical
instruments.
dangerous
mutation
cancer
lead
bones
bacteria
sterilise
WORD SELECTION
bacteria
cancer
mutation
dangerous
bones
sterilise
lead
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Gamma and X-ray Simulations

• Gamma Radiation - Powerpoint presentation by
  Tiernan Mines (L6th 2005)
• Making X-rays - Colorado
• X-rays - Fluoroscope demo Colorado
• BBC Bitesize Revision
• Gamma X-rays

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Gamma rays and X-rays Notes questions from pages
80/284 81/285

1. Explain how an X-ray photograph is produced.
2. What is the source of gamma rays? How can they be
   stopped?
3. Give three uses of gamma rays.
4. Copy and answer questions (a) and (b) on page
   80/284.
5. In what ways are X-rays and gamma rays dangerous?
   What safety precautions can be taken?
6. Copy and answer question (d) on page 81/285.
7. Copy the Key Points on page 81/285.
8. Answer the summary questions on page 81/285.

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Gamma rays and X-rays ANSWERS

• In text questions
• A crack is a gap that
• X-rays can pass through.
• Yes.
• To keep the light out without stopping the
• X-rays.

• Summary questions
• (a) Penetrate (b) Absorb
• (c) Damage
• (a) To make an image of the patients bones on
  the film.
• (b) To stop light from affecting the film.
• (c) To prevent damage by the
• X-rays to the parts of the body not being
  X-rayed. High doses can kill living cells and low
  doses can cause cell mutation and cancerous
  growth.

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Ultraviolet
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Ultraviolet (UV)

• Ultraviolet has a wavelength of typically 100
  nanometres.
• (0.000 000 1 m, a ten millionth of a metre).
• UV is produced from very hot objects like the Sun
  or from special electrical tubes.
• Most of the Suns ultraviolet radiation is
  absorbed by the Ozone layer in the upper part of
  the Earths atmosphere.
• UV is also stopped by glass.

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Uses of ultraviolet

• Ultraviolet is used in
• Fluorescent lamps including energy efficient
  light bulbs
• Security devices
• Dentistry
• Pest control
• Astronomy

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Safety with ultraviolet

• The Suns ultraviolet light is responsible for
  sun tan.

Too much exposure to UV is dangerous and can lead
to skin cancer.
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Visible light
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Visible light

• Visible light has wavelengths ranging from
• 400 nanometres (violet)
• to
• 700 nanometres (red).
• Visible light is emitted from hot objects like
  the Sun.

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The spectrum of white light
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(No Transcript)
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Electromagnetic waves and substances

• Electromagnetic waves may be REFLECTED at the
  surface of a substance.
• The type of surface and the wavelength of the
  waves determine if the waves are totally or
  partly reflected or not reflected at all.

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• Some or all of the waves that go into a substance
  may be ABSORBED by it.
• The substance becomes hotter due to the energy it
  gains from the absorbed radiation.
• The radiation may also cause an alternating
  electric current within the substance of the same
  frequency as the radiation itself.

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• The waves that are not absorbed by a substance
  are TRANSMITTED by it.
• The type of substance and the wavelength of the
  waves determine whether the waves pass through
  it.

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Choose appropriate words to fill in the gaps
below Ultraviolet radiation has a _______
wavelength than _______ light and is responsible
for sun tan. UV is dangerous and can cause ______
cancer. Visible light is made up of the colours
of the _________. Red light has the _________
wavelength, violet has the _________
frequency. Electromagnetic radiation can be
reflected, absorbed or ___________ by substances.
What happens depends on the ___________ of the
electromagnetic waves.
visible
shorter
skin
spectrum
highest
longest
transmitted
wavelength
WORD SELECTION
highest
visible
longest
wavelength
spectrum
shorter
skin
transmitted
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Simulations

• Vend diagram quiz comparing light and sound waves
  - eChalk
• Lasers - PhET - Create a laser by pumping the
  chamber with a photon beam. Manage the energy
  states of the laser's atoms to control its
  output.
• Lasers - Colorado
• Fibre optic reflection - NTNU
• BBC Bitesize Revision
• Optical fibres
• Ultraviolet Infra-red

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Light and ultraviolet radiation Notes questions
from pages 82/286 83/287

1. What is white light made of?
2. Copy Figure 1 on page 82/286.
3. What determines the colour of light? Explain how
   a colour filter works.
4. What is ultraviolet radiation? How does it
   compare with visible light?
5. Explain how ultraviolet radiation can cause some
   substances to emit light.
6. What are the dangers of ultraviolet radiation?
7. Explain the connection between ultraviolet
   radiation, the ozone layer and CFCs.
8. Explain, with the aid of a copy of Figure 2, the
   various ways in which electromagnetic waves
   interact with substances.
9. Copy and answer questions (a), (b), (c) and (d)
   on pages 82/286 and 83/287.
10. Copy the Key Points on page 83/287.
11. Answer the summary questions on page 83/287.

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Light and ultraviolet radiation ANSWERS

• In text questions
• Shorter
• When ultraviolet radiation is directed at the
  ink, the ink absorbs it and emits light as a
  result.
• Absorbed.
• The ink is invisible until you shine UV light on
  it. Then the ink absorbs and emits it as light so
  objects can be marked with the security pen and
  ownership can be checked.

• Summary questions
• (a) Red, blue (b) Ultraviolet radiation
• (c) White
• 2. (a) It harms the skin and can cause skin
  cancer. It damages the eyes and can cause
  blindness.
• (b) (i) It absorbs most of the ultraviolet
  radiation from the Sun.
• (ii) Ultraviolet radiation causes sunburn.
  Suncreams stop UV radiation reaching the skin.
  Suncream absorbs the UV radiation that passes
  through the ozone layer.
• 3. Reflected bounce off surface.
• Transmitted pass through a substance.
• Absorbed substance gains energy from
  radiation and gets hotter. The radiation may
  cause an alternating current the same frequency
  as itself.