Electromagnetic Waves

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  • Electromagnetic Waves
    • Radiowaves
      • Uses
        • Broadcasting
          • TV and FM Radio broadcasting
            • 10cm-10m
            • To get reception, you have to be in direct sight of the transmitter
            • Cannot diffract or go around hills; doesn't go far through tunnels
        • Communication
          • Long-wave radio
            • 1-10km
            • Can be receieved halfway around the world due to diffraction
            • bend around the surfaces of the Earth, and around hills, through tunnels etc.
              • Can be receieved halfway around the world due to diffraction
          • Short-wave radio
            • 10-100m
            • Can be receieved from a long distance
            • due to the waves reflecting off the ionosphere
              • Electrically charged layers in the Earth's upper atmosphere
    • Microwaves
      • Uses
        • Cooking
          • Microwaves are absorbed by the water molecules in the food
            • They penetrate a few cm into the food before being absorbed
              • The energy is then conducted or convected to other parts of the food
        • Satellite transmissions
          • 1-10cm
          • Use microwaves that move through the Earth's watery atmosphere without being absorbed
          • For a satellite TV, the signal from the transmitter is transmitted to space
            • There it is picked up on by a satellite receiver dish orbiting thousands of kilometers above the Earth
              • The signal is then transmitted back down to Earth in different directions
                • From that it is received from a satellite dish on the ground
      • Dangers
        • Internal heating of body tissue
    • Infrared
      • Dangers
        • Skin burns
      • Uses
        • Heaters
          • ALL objects give off IR - The hotter the object, the more IR it gives off
        • Night-vision equipment
          • Turns IR into electrical signals which is displayed on screen as a picture
          • Allows things that would be otherwise hidden in the dark, e.g. criminals, to be seen
        • remote controls for TVs
        • short-range communications, for example between mobile phones
    • Visible light
    • Ultraviolet
      • Uses
        • UV is absorbed and light is emitted in fluorescent lighting
          • Nearly all of the UV radiation is absorbed by a phosphor coating on the inside of the glass
        • Fluorescent lights are more energy efficient than filament light bulbs
      • Dangers
        • Damage surface cells
        • Blindness
        • Cell mutations and cancer
          • Due to UV radiation being ionising - able to knock electrons off atoms
        • Safety precautions
          • Wear sunscreen with UV filters
          • Stay out of strong sunlight
        • Sun burn/ skin cancer
    • X-Rays
      • Uses
        • View the internal structure of objects (like bodies
        • Produce x-ray images
          • X-ray radiation is directed through the body onto a detector plate
          • X-rays pass easily through flesh but not through denser materials like bones or metal
          • The brighter bits of the x-ray image is where less radiation can get through
        • Airport security
      • Dangers
        • Cell mutation and cancer
        • Safety precautions
          • Lead aprons and shields
          • Minimum exposure to the radiation
      • Given off by stars
      • Barium meal
        • Drink of barium sulphate which will absorb the x-rays, so the patient's intestines will show up clearly on a x-ray image
    • Gamma Rays
      • Uses
        • Sterilising medical equipment
          • Gamma rays kill the microbes
          • Better than boiling plastic instruments as they will likely be damaged by the high temperatures
        • Sterilising food
          • By killing the microbes
          • Keeps food fresher for longer without freezing it or cooking it or preserving it some other way
          • Food is not radioactive afterwards - safe to eat
        • Can kill cancer cells (radiotherapy)
      • Dangers
        • Cell mutation
        • Tissue damage
        • Cancer
        • Strongly ionising and carry the most energy
        • Penetrate further in the body
        • Safety precautions
          • Kept in a lead-lined box when not in use
          • Minimum exposure time
          • Protective clothing

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