Topic 6 Waves

• What are longitudinal and transverse waves?

  Longitudinal: direction of oscillation is parallel to the direction of energy transfer (e.g. sound). Consists of compressions & rarefactions

  
  

  Transverse: direction of oscillation is perpendicular to the direction of energy transfer (e.g. water waves, light, EM waves)
• What is wavelength, time period and frequency?

  Wavelength (m) - length of one complete wave

  Time period (s) - time taken for one wave to pass

  Frequency (hz) - number of waves pass every second
• What is the equation for wavespeed?

  Wavespeed (m/s) = frequency (hz) x wavelength (m)
• What does sound waves do?

  They cause our eardrums to vibrate, which sends signals to our brain.
• What is the human hearing range?

  20Hz to 20k Hz. If f>20k Hz: Ultrasound
• What happens when sound meets a boundary between two mediums?

  Some sound is transmitted, while some is reflected
• How have waves proved that the Earth's core is not solid?

  Seismic P-waves (longitudinal) pass through the centre of the Earth while S-waves (transverse) do not, which suggests that Earth has a molten core
• What is specular reflection?

  When light reflects off a smooth surface
• What is diffuse reflection?

  When light scatters off a rough surface
• What is the Electromagnetic spectrum?

  Radio waves, Microwaves, Infa-red, Visible light, Ultra violet, Xrays and Gamma rays

  As you go to the right, wavelength becomes shorter, the frequency becomes higher and there's more energy
• What are all EM waves emitted and absorbed by?

  Electrons (apart from gamma which are emitted by nuclei)
• What happens if the energy of a wave is too high?

  It can cause an electron to leave its atom, leaving an ion which results in ionising radiation. UV, X-rays and gamma are ionising radiation
• What is refaction?

  When waves enter a new medium their speed changes as does their angle

  
• What do lenses do?

  They use refraction to make light rays converge or diverge
• What type of lens is this?

  Convex

  
• What type of lens is this?

  Concave

  
• How do we see different colours?

  We perceive different colours when different wavelengths of lights are absorbed by the retina
• What is a blackbody?

  A theoretical object that perfectly absorbs and emits all wavelengths of radiation
• What happens if the rate of absorption is greater than the rate of emission?

  Its temperature increase. But this then in turn increases the rate of emission.