4 LESSON_Q2

• Disturbances in a field that carry energy and do not require a medium to travel
• Waves that lie at the ends of the visible spectrum

  • X-rays
  • Gamma rays
• Visible spectrum


  The only electromagnetic waves perceived by the human eye
• White light is made up of a variety of colors
• When light passes through a prism, it is separated into its constituent colors: red, orange, yellow, green, blue, indigo and violet (ROYGBIV)
• Visible spectrum


  The range of wavelengths of white light that the human eye is sensitive to (4 x 10-7 m to 7 x 10-7 m)
• Wavelengths of the different colors of light

  • Violet - Indigo (390 - 455 nm)
  • Blue (455 - 492 nm)
  • Green (492 - 577 nm)
  • Yellow (577 - 597 nm)
  • Orange (597 - 622 nm)
  • Red (622 - 700 nm)
• Activity: Screen the UV out

  1. Cut newspaper to fit in Ziploc bag

  2. Draw lines to divide bag into 3 parts

  3. Apply sunscreen on left part

  4. Cover middle part with black paper

  5. Leave right part exposed

  6. Place bag in sunlight

  7. Observe changes
• The activity demonstrates the effects of ultraviolet (UV) radiation
• Ultraviolet radiation is the next part of the electromagnetic spectrum after visible light
• Procedure

  1. Cut a piece of newspaper to fit snugly inside a Ziploc snack bag

  2. Outside the snack bag, draw two lines with a marker dividing the bag into three equal parts from the top of the bag to the bottom

  3. Apply a thin coat of sunscreen in the leftmost part

  4. Cover the middle part with black construction paper

  5. The right part should be left fully exposed

  6. Place the snack bag in an area fully exposed to sunlight

  7. Recover the snack bag in the afternoon
• Ultraviolet radiation


  Lies just beyond the violet end of the visible spectrum, has shorter wavelengths than visible light and carries more energy
• The sun is our main source of ultraviolet (UV) radiation but there are also artificial sources of UV light
• Uses of UV radiation

  • Banks use UV lamps to check signatures on passbooks
  • Hospitals use UV to sterilize medical instruments
  • Some washing powder contains fluorescent chemicals which glow in sunlight
• Effects of UV radiation

  Produces Vitamin D in the skin and gives us a tanning effect, but could burn the skin, hurt our eyes, and cause skin cancer
• Ways to protect yourself from UV radiation

  • Wear sunscreen
  • Wear protective clothing
  • Seek shade
  • Avoid peak sun hours
• 1. rays


  Have shorter wavelengths but carry higher energy than UV, can penetrate flesh but not bones, used in X-ray photography to help doctors look inside the body
• 1. rays are dangerous as they can damage healthy living cells of the body, frequent exposure should be avoided
• Gamma rays


  Lie at the other end of the electromagnetic spectrum, shortest in wavelength and highest in frequency, carry the highest amount of energy, can kill living cells
• Gamma rays are used to treat cancer through radiotherapy and for sterilization of medical equipment
• Waves in the Electromagnetic (EM) spectrum

  • Radio waves
  • Microwaves
  • Infrared waves
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• Applications/Uses of EM waves

  • Radio waves: Radio and television communication

  Microwaves: Satellite television and communication, Cooking food

  Infrared waves: Remote control, household electrical appliances

  Visible light: Artificial lighting, screen of electronic devices

  Ultraviolet: Sterilization, fluorescence

  1. rays: Medical use, engineering applications

  Gamma rays: Medical treatment, sterilization of medical equipment