EM Waves, Matter & Atoms | Physics for Grade 10 PDF Download

Interaction of Different Substances

• Transmitted
• Absorbed
• Reflected
• Refracted

When 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 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 & 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 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