AQA GCSE Physics 1b5 Electromagnetic Waves

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AQA GCSE Physics 1b-5Electromagnetic Waves

• GCSE Physics pages 78 to 93

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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.
• When radiation is absorbed the energy it
  carries makes the
• substance which absorbs it hotter and may create
  an alternating current with the same frequency as
  the radiation itself.
• 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.
• Radiowaves, microwaves, infra red and visible
  light can be used for communication.
• Microwaves can pass through the Earths
  atmosphere and are used to send information to
  and from satellites and within mobile phone
  networks.

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The electromagnetic spectrumNotes questions from
pages 78 79

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

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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 and X-rays Notes questions from pages
80 81

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

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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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Light and ultraviolet radiation Notes questions
from pages 82 83

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

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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) Ultraviloet 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.

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Infra-red, microwaves and radio waves Notes
questions from pages 84 85

• What type of objects emit infra-red radiation?
  How can infra-red radiation be dangerous?
• Why are microwaves so called?
• Write a sentence in each case about four uses of
  infra-red radiation and two uses of microwaves.
• Copy and answer questions (a) and (b) on page 84.
• State the frequency range of radio waves and how
  they compare with microwaves.
• Explain what happens in an aerial when radio
  waves are (a) transmitted and (b) received.
• Copy the Key Points on page 85.
• Answer the summary questions on page 85.

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Infra-red, microwaves and radio waves ANSWERS

• In text questions
• Between light and microwaves
• (i) Yes
• (ii) They cause the microwave oven to overheat,
  because metal objects absorb microwave radiation
  very easily.

• Summary questions
• (a) Radio waves, light
• (b) Microwaves, infra-red radiation.
• (a) Infra-red (b) Microwave
• (c) Radio (d) Infra-red
• 3. An alternating voltage applied to an aerial
  produces radio waves which cause a small
  alternating voltage in the receiver aerial when
  they arrive there.

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Communications Notes questions from pages 86 87

• Copy out the waveband table on page 86.
• Why is the quality of communication better with
  the higher frequency radio bands?
• Draw a diagram and explain how the ionosphere is
  used in radio communication.
• What are optical fibres? Draw a diagram showing
  how light travels through an optical fibre.
• What advantages does optical fibre communication
  have over radio wave communication?
• Copy and answer questions (a), (b), (c) and (d)
  on pages 86 and 87.
• Copy the Key Points on page 87.
• Answer the summary questions on page 87.

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Communications ANSWERS

• In text questions
• Satellite TV signals are from a transmitter on a
  satellite terrestial TV signals are from
  transmitters on the ground.
• The signals pass into space because they do not
  reflect from the ionosphere.
• The signals go straight through the atmosphere
  above you and into space.
• Optical fibres are only suitable for fixed links.

• Summary questions
• (a) Radio waves (b) Microwaves
• (c) Microwaves, radio waves.
• 2. (a) Local radio stations transmit radio waves
  that are easily absorbed by the atmosphere so
  they cant travel far.
• (b) The signals are carried by light or
  infra-red radiation, which cant be detected
  outside the fibre surface because it only enters
  or leaves at its ends.
• 3. Because microwaves are not reflected by the
  ionosphere. They pass straight through.

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Analogue and digital signals Notes questions
from pages 88 89

• Define what is meant by a (a) digital signal and
  (b) analogue signal. Copy Figure 1 on page 88
  below your answers.
• Give some examples of both types of signal.
• Explain the advantages of using digital signals
  in communication.
• Explain what is meant by (a) a carrier wave, (b)
  amplitude modulation and (c) frequency
  modulation.
• Copy and answer questions (a), (b) and (c) on
  pages 88 and 89.
• Copy the Key Points on page 89.
• Answer the summary questions on page 89.

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Analogue and digital signals ANSWERS

• In text questions
• To convert an analogue signal into a digital
  signal.
• Digital.
• Digital.

• Summary questions
• (a) Analogue, carrier. (b) digital, analogue.
• (c) Digital.
• A carrier wave, B signal, C transmitter,
• D receiver.
• 3. Analoge to digital The voltage of the
  analogue waveform is sampled (that is measured)
  automatically many times each second. Each
  voltage measurement is then turned electronically
  into a corresponding sequence of pulses. The
  digital signal consists of successive pulse
  sequences (that is a digital signal).
• Digital to Analoge Each sequence of pulses
  of the digital signal is turned into a
  corresponding analogue voltage measurement. The
  analogue waveform consists of successive analogue
  voltage measurements.

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Microwave issues Notes questions from pages 90
91

• Answer question 1 on page 90.
• Answer question 2 on page 91.

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Microwave issues ANSWERS

• The higher the power the longer the range.
  Submarines could be detected further away using
  high power radar.
• (a) Microwave radiation penetrates their skulls
  more than older skulls because their skulls are
  thinner. Also, smaller heads heat up more easily
  than bigger heads.
• (b) They could find out if people with brain
  tumours used mobile phones (e.g. average use per
  day per person) more than the average healthy
  person.
• (c) They could use a brain scanner to compare
  the brains of people who used mobile phones a lot
  with non-users. They could conduct other tests
  as well, such as memory tests. They could also
  compare the brains of dead rats exposed to
  microwaves with those of unexposed rats.
• (d) The driver needs to concentrate on driving
  and is distracted by using a mobile phone at the
  same time.

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How Science Works ANSWERS

• The longer the wavelength of light the higher the
  voltage.
• The reading after 80 seconds.
• The anomaly should be investigated further.
• A line graph. Both variables are continuous.