♡ Topic 4_ Waves ♡

• Waves transfer energy and information but do not transfer matter
• Two types of waves are transverse and longitudinal
• Transverse wave:

  • Oscillations are perpendicular to the direction of energy transfer
• Longitudinal wave:

  • Oscillations are parallel to the direction of energy transfer
• Examples of transverse waves:

  • Electromagnetic waves
  • Seismic s-waves
• Examples of longitudinal waves:

  • Sound waves
  • Seismic p-waves
• Two parts of a longitudinal wave are compressions and rarefactions
• Two parts of a transverse wave are peaks and troughs
• Wave's amplitude:

  • Maximum displacement of a point on a wave from its undisturbed position
• Wavelength:

  • Distance from a point on a wave to the same position on the adjacent wave
  • Most commonly peak to peak or trough to trough
• Frequency of a wave:

  • Number of waves that pass a given point each second
• Unit used for frequency:

  • Hertz, Hz
• Wave speed:

  • Speed at which energy is transferred through a medium
• Wave velocity:

  • Equal to the product of the wavelength and frequency of the wave
  • Measured in metres per second
• Equation for calculating wave speed:

  • Wave Speed = Frequency x Wavelength
  • Speed (m/s), Frequency (Hz), Wavelength (m)
• Period of the wave:

  • Length of time it takes for one full wave to pass through a point
• Sound waves travel through a solid by the particles in the solid vibrating and transferring kinetic energy through the material
• The human ear works in the following steps:

  • The outer ear collects the sound which travels into the ear
  • The sound waves cause the eardrum to vibrate at the same frequency
  • This is amplified by three ossicles (small bones)
  • This causes the hair in the cochlea to vibrate
  • The cochlea converts the vibrations into electrical signals
  • The signals are passed to the brain through the auditory nerve
  • The brain converts the electrical signals into sound
• The frequency range of human hearing is 20 Hz - 20kHz (1kHz = 1000 Hz)
• An ultrasound wave is a sound wave with a frequency greater than 20,000 Hz
• Sound of frequencies less than 20Hz is called Infrasound
• Seismic waves are produced by earthquakes and they produce both P-waves and S-waves
• P waves are longitudinal waves
• S waves are transverse waves
• A difference between the mediums that P-waves and S-waves can travel through is:

  • P-waves travel through both solids and liquids
  • S-waves only travel through solids (not liquids)
• The significance of P and S waves is that they provide evidence that the Earth has a liquid core; only P waves produced by an earthquake can be detected on the other side of the globe
• Echo sounding is a technique used to detect objects in deep water and measure water depth by emitting, reflecting, and detecting high frequency sound waves, then calculating distances using the time difference between emission and detection, alongside wave speed
• Sonar works by emitting ultrasound waves that reflect off boundaries and their echoes are detected, then using the known speed of ultrasound and the time it takes to detect the echoes to calculate the distance travelled, halving it to find the distance between emitter and boundary
• Foetal scanning works by sending an ultrasound wave into the patient's body, which passes through and reflects off organs and tissue, then using the reflected ultrasound waves to produce an image of the foetus; ultrasound is safe and does not damage cells
• Equation to calculate wave speed: Wave Speed = Frequency x Wavelength

  • Speed (m/s)
  • Frequency (Hz)
  • Wavelength (m)
• Word used to describe when a wave bounces off a surface: Reflection
• Definition of the normal in terms of reflection and refraction: A vertical imaginary line which is perpendicular to the boundary
• What occurs when light is reflected off a boundary: It bounces off a smooth flat surface so that the angle of incidence is equal to the angle of reflection
• Definition of refraction: Refraction is the change in speed of a wave as it reaches a boundary between two media, usually resulting in a change in direction
• What occurs when light is refracted at a boundary:

  • The light changes speed and direction in the new medium
  • If the new medium is more dense, the light will travel slower and bend towards the normal
  • If the new medium is less dense, the light will travel faster and bend away from the normal
• When entering a denser material, light waves slow down and bend towards the normal
• When entering a less dense material, light waves speed up and bend away from the normal
• How refraction can be measured: The angle of incidence, i, and angle of refraction, r, can be measured and compared. All angles are measured relative to the normal
• Effects of absorption of different wavelengths of waves in different mediums:

  • Some materials behave differently depending on the wavelength
  • An example is glass which will transmit visible light, but reflect UV light
• How sound waves travel through a solid: The particles in the solid vibrate and transfer kinetic energy through the material