EM waves

• Facts of EM waves:

  • They are all transverse waves
  • They are made of oscillating electric and magnetic field and do not carry electrical charges
  • They travel at 3 x 10^8 m/s in a vacuum
  • Wave speed = frequency x wavelength
  • Vacuum to other medium: wavelength and speed change, frequency same
  • Undergoes reflection and refraction and transfers energy
  • All bodies emit range of EM waves
• Types of EM waves:

  1. Radio waves (Longest, lowest frequency)
  2. Microwaves
  3. Infra red
  4. Visible light
  5. Ultraviolet (ionising)
  6. X-rays (ionising)
  7. Gamma rays (ionising, shortest, highest frequency)
• Radio waves:

  Uses:

  • Transmitting of infomation by radio
  • Radio telescopes for study of celestial objects
  • Radio Frequency Identification (RFID) aka condo access card
• Microwave:

  Uses:

  • WiFi
  • Mobile phone communication
  • Global positioning system (GPS)
  • Satellite communication
  • Radar
  • Cancer treatment
• Infra-red:

  Uses:

  • Oven to cook food
  • Data transfer (faster than microwaves) in phones, laptops and long distance fibre-optic cables
  • Remote control (📺)
  • Camera auto-focusing (📸)
  • Thermometers (🔥)
• Visible light:

  Uses:

  • Photography 📸
  • Transmission of data (optic fibre transmit light to illuminate organs)
  • Polymerisation using light (⚗)
  • Photographic film (🎞️)
• Ultraviolet:

  Uses:

  • Disinfecting and sterlisation (🦠)
  • Vitamin D for muscles, bone and immunity
  • Anti-forgery features (💵)

  Harmful effect:

  • Skin cancer and premature aging from overexposure
• X-rays:

  • Body part which absorb more X-ray appear brighter, doctor can see internal structures
  • Computed Tomography (CT) can show 3D image of scanned volume
  • Useful for killing cancer cells and scanning for manufacturing effects and prohibited items
• Gamma rays:

  • Kills germs in food and sterilise medical equipment
  • Radiotherapy and manufacturing defects
  • Can be used to treat cancer through gamma knife radio surgury where hundreds of gamma rays are directed at a precise point of the brain
• Harmful effects of EM waves: Ionising radiation:

  • High energy EM waves penerate our bodies more easily
  • High frequency wave can knock an electron out of body cell, ionising it
  • Charged ion does not behave normally and can disrupt chemical process and biological system, even causing death as a result
• Harmful effects of EM waves: heating

  • Over-exposure causes skin cancer and premature aging
  • Precautions should be taken to protect against UV rays