LIGHT

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CHAPTER 27

• LIGHT OTHER ELECTROMAGNETIC WAVES

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• Electromagnetic Waves
• are transverse waves produced by the motion of
  electrically charged particles.
• An electromagnetic wave consists of electric
  field and magnetic field waves at right angles to
  each other.

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• Electromagnetic Waves
• These waves vary depending on frequency and
  wavelength.
• They dont need a medium to travel.

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• Electromagnetic Waves
• Their speed varies with the change in medium.
• All electromagnetic waves travel at the same
  speed through a vacuum (3 x 108 m/s). Their
  wavelength and frequency are different.

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• Electromagnetic Waves
• They carry energy and have momentum.
• They have both wave and particle like behavior.

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• RADIO WAVES
• MICROWAVES
• INFRARED
• VISIBLE LIGHT
• ULTRA VIOLET LIGHT
• X-RAYS
• GAMMA RAYS

FREQUENCY INCREASES
WAVELENGTH DECREASES
ENERGY INCREASES
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LIGHT

• Light is composed of tiny particles.
• These particle-like bundles of radiation are
  called photons.

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LIGHT

• Higher the frequency of the electromagnetic
  waves, the greater the energy of the wave.
• Light produces interference patterns like water
  waves.

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• RADIO WAVES
• Have low frequency
• and long wavelengths.
• They have the lowest
• photon energy.

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• RADIO WAVES
• Radio waves are used to transmit radio and TV
  signals.
• They are also used in cellular phones and
  cordless phones.

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• RADIO WAVES
• The process of varying radio waves is called
  modulation.
• Voice, light images, computer information, and
  music can be used
• for modulation.

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OTHER USES OF RADIO WAVES

• Communications
• Navigation and defense equipment
• Weather Forecasting
• 4.TV signals
• 5. AM and FM radio signals
• 6. Airport air traffic controllers
• 7. Radar used by police cars

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INFRA RED RADIATION

• Has a wavelength slightly longer than visible
  light.
• Your skin feels warm
• outside because your
• skin is absorbing
• infrared radiation
• from the sun.

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• A thermogram is produced by measuring the
  infrared radiation given off by different parts
  of the body.
• Tumors are detected by thermograms because they
  are warmer than other parts of the body.

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• Some security systems are designed to detect
  objects giving off infra red radiation and to
  respond by activating an alarm.

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• Infrared radiation are used to warm and dry
  objects.
• Infra red lamps in
• some restaurants
• keep the food
• warm until served.

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• Infrared images obtained from sensors on
  airplanes can yield important information on the
  health of crops and help us see
• forest fires even
• enveloped in an
• opaque layer of
• smoke.

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Increasing Wavelength Decreasing Frequency
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VISIBLE LIGHT

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VISIBLE LIGHT

• It is the only part of the electromagnetic
  spectrum that we can see.
• Violet Color has a smaller wavelength than red
  color.

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ULTRA VIOLET RADIATION

• They have higher frequency than visible light.
• Exposure to UV radiation enables skin cell to
  manufacture vitamin D, which is needed for
  healthy bones and teeth.

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ULTRA VIOLET RADIATION

• Ultra violet lamps are used in hospitals to kill
  bacteria and viruses, and to sterilize surgical
  instruments.

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ULTRA VIOLET RADIATION

• UV rays are used to kill microorganisms in food
  and on hospital equipment.
• Some minerals like fluorite and scheelite become
  fluorescent when exposed to UV light.
  Fluorescence occurs when a material absorbs UV
  radiation and re-emits visible light.

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EXCESS OF ULTRA VIOLET RADIATION

• Lead to sagging, dry skin and even skin cancer.
  Sunscreen contains chemicals that absorb UV
  radiation before they penetrate your skin.

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Crest

• Ozone is found in the Earths outer atmosphere
  and it protects us from most of the suns UV
  radiation.

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Ozone is produced naturally through
photochemical reactions and electric discharge
reactions (lightning) in the atmosphere.
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• Ozone depletion is caused by chemicals (CFC)
  that break down ozone. These chemicals are found
  in hair sprays, refrigerants etc.

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X-RAYS

• X-rays have shorter wavelength and
• higher frequency
• than UV radiation.
• They possess enough energy to penetrate dense
  objects like skin and muscles.

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X-RAYS

• When X-rays hit more dense objects they are
  absorbed.
• X-rays are used to scan luggage and packages
  without opening
• them at the
• airport.

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GAMMA RAYS

• Have the highest frequency and are the most
  penetrating.
• Gamma rays are
• emitted
• from the nuclei of
• radioactive atoms.

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GAMMA RAYS

• Earth receives some gamma rays from space.
• They can be used to kill cancerous cells.

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GAMMA RAYS

• People using gamma radiation for treatment suffer
  side affects like nausea, hair loss, and fatigue
  because healthy cells are also damaged.

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THINK ABOUT IT

• 1.Describe at least two ways in which
  electromagnetic waves differ from mechanical
  waves.
• 2.Describe at least one helpful use for each of
  the six main types of electromagnetic radiation.