Waves

Waves

1. Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred

   • Transverse waves In transverse waves, the oscillations (vibrations) are at right angles to the direction of travel and energy transfer Light and other types of electromagnetic radiation are transverse waves. All types of electromagnetic waves travel at the same speed through a vacuum, such as through space.
   • Longitudinal waves In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer. Sound waves and waves in a stretched spring are longitudinal waves. P waves (relatively fast moving longitudinal seismic waves that travel through liquids and solids) are also longitudinal waves. Longitudinal waves show area of compression and rarefaction. In the animation, the areas of compression are where the parts of the spring are close together, while the areas of rarefaction are where they are far apart.

2. Some waves must travel through a substance. The substance is known as the medium and it can be solid, liquid or gas. Sound waves and seismic waves are like this. They must travel through a medium, and it is the medium that vibrates as the waves travel through.

3. Other waves do not need to travel through a substance. They may be able to travel through a medium, but they do not have to. Visible light, infrared rays, microwaves and other types of electromagnetic radiation are like this. They can travel through empty space. Electrical and magnetic fields vibrate as the waves travel.

4. Wavelength The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the crest of one wave to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave.

5. Refraction and diffraction

   • Waves can be refracted and diffracted. You do not need to know how this happens for your examination, but you should know what refraction and diffraction are.
     • Refraction Sound waves and light waves change speed when they pass across the boundary between two substances with different densities, such as air and glass. This causes them to change direction and this effect is called refraction. There is one special case you need to know. Refraction doesn't happen if the waves cross the boundary at an angle of 90° (called the normal) - in that case they carry straight on.
     • Diffraction When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is called diffraction.

6. Reflection

   • Sound waves and light waves reflect from surfaces. When waves reflect, they obey the law of reflection. the angle of incidence equals the angle of reflection