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Interaction of Different Substances

When EM waves move from one medium to another the waves might be:

  • Transmitted
  • Absorbed
  • Reflected
  • Refracted

When waves move from one medium to another they can be transmitted, reflected, refracted or absorbedWhen waves move from one medium to another they can be transmitted, reflected, refracted or absorbed

  • The material interacts differently with different parts of EM spectrum because of the difference in wavelength
  • Whilst some wavelengths might be transmitted, others might be reflected, refracted or absorbed
  • Which of the interactions happen depends on:
    • The wavelength of the waves
    • The material the wave is travelling through
  • For example, glass will:
    • Transmit and/or refract visible light
    • Absorb UV radiation
    • Reflect IR radiation

Refraction of EM Waves

  • Some effects, for example, refraction, are due to the difference in velocity of the waves in different substances
  • Although all electromagnetic waves travel at the same speed in a vacuum, when they encounter certain materials (water, glass, oil) they will slow down
    • How much they slow down depends on the material
    • This slowing of electromagnetic waves causes them to refract
  • A simple example of this is the refraction of visible light when it enters (or leaves) a glass block, although other electromagnetic waves can also refract

When electromagnetic waves pass through matter, their interactions slow them down causing them to refractWhen electromagnetic waves pass through matter, their interactions slow them down causing them to refract

Wavefront Diagrams

  • When a wave hits a different medium the different parts of the wave enter the medium at different times
    • Hence, this leads to a change in speed
  • The difference in speed between the parts of the wave in the first medium and the parts in the second medium causes the wave to bend
    • Hence, this leads to a change in direction
  • Refraction can be represented using wavefront diagrams, as shown below:

EM Waves, Matter & Atoms | Physics for Grade 10

The different parts of the wave enter the second medium at different times causing the wave to bend

EM Waves & Atoms

  • Atoms can interact with electromagnetic (EM) waves in one of two ways, they can be:
    • Absorbed
    • Emitted
  • When an EM wave hits an atom, it can be absorbed by one of the electrons giving it energy
    • This causes the electron to move up to a higher energy level
  • If an electron moves down to a lower energy level it will emit an EM wave in the process
    • In this way, atoms can absorb and emit electromagnetic waves over a wide range of frequencies

The electrons orbiting atoms can absorb and emit EM waves by moving between different energy levelsThe electrons orbiting atoms can absorb and emit EM waves by moving between different energy levels

  • The energies associated with electron transitions tend to be in the visible and ultraviolet range (and sometimes X-rays)
  • Higher energies (ie. gamma rays) can only be achieved when EM waves interact with the nucleus
    • The nucleus of an atom can absorb and emit EM waves in a similar way to electrons
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