4. Waves

4. Waves

1. 4.1 Waves and vibrations

   • EM waves are oscilliating electric and magnetic fields that progress through space without the need for a substance.
   • Longitudinal waves
     • The directon of vibration of the particles is parallel to the direction in which the wave travels
     • Examples include : slinky, and sound waves
   • Transverse waves
     • The direction of vibration of the particles is perpendicular to the direction in which the wave travels
     • Examples include EM waves and waves on a string or wire
   • Polarisation
     • Transverse waves can be PLANE POLARISED. Which is when the vibrations stay in one plane only. If the vibrations change from one plane to anothert this means that they are UNPOLARISED
     • Longitudinal waves cannot be polarised

2. 4.2 Measuring waves

   • Key terms
     • The displacement of a vibrating particle is its distance and direction from it's equilibrium position
     • The amplitude of a wave is the max. displacement of a vibrating particle from the equilibrium position.
     • The wavelength is the least distance between two adjacent particles. e.g distance between adjacent crests
     • One cycle of a wave is from one max. displacement to the next
     • The period of a wave is the time for one complete wave to pass a fixed point
     • The frequency of a wave is the number of complete waves passing a point per second
   • Phase difference between two particles vibrating at the same frequency is the fraction of a cycle between the vibrations of the two particles
   • wave speed, c = f x wavelength

3. 4.3 Wave properties 1

   • Reflection
     • The dish design
       • Satellite dishes in Europe need to point south, because the satellites orbit the earth directly above the equator. The bigger the dish, the better the signal because it can reflect more waves onto the aerial. The bigger dish reflects the waves to a smaller focus because it diffracts the waves less. The dish therefore needs to be aligned more carefully than a smaller dish, otherwise it won't focus the waves onto the aerial.
     • Straight waves directed at a certain angle to a hard flat surface reflect off at the same angle. The angle between the reflected wavefront and the surface is the same as the angle of the incident wavefront and the surface.
   • Refraction
     • When waves pass across a boundary at which the wave speed changes, the wavelength also changes. If they approach at an angle they also change direction as well as speed. Usually to a substance of higher density eg. air to water
   • Diffraction
     • when light passes through a gap or around an obstacle the waves spread out. The narrower the gap, the more the waves spread out. The longer the wavelength, the more the waves spread out.

4. 4.4 Wave properties 2

5. 4.5 Stationary and progressive waves

6. 4.6 More about stationary waves on springs

7. 4.7 Using an oscilloscope

Imagens e arquivos do mapa