Topic 4 - Waves

• Complete this sentence.

  Waves transfer *****

  and*********but do not transfer*****Waves transfer energy and information but do not transfer matter
• What are the two types of waves?

  transverse and longitudinal
• What is a transverse wave?

  Wave in which the oscillations are perpendicular to the direction of energy transfer.
• What is a longitudinal wave?

  A wave in which the vibration of the medium is parallel to the direction of energy transfer.
• Give two examples of transverse waves.

  1. Electromagnetic waves

  2. Seismic s-waves
• Give two examples of longitudinal waves.

  1. Sound waves

  2. Seismic p-waves
• What are the two parts of a longitudinal wave called?

  compressions and rarefactions
• What are the two parts of a transverse wave called?

  peaks and troughs
• What is a wave's amplitude?

  The maximum displacement of a point on a wave from its undisturbed position.
• What is wavelength?

  ● The distance from a point on a wave to the same position on the adjacent wave

  ● Most commonly peak to peak or trough to trough
• What is the frequency of a wave?

  the number of waves that pass a given point each second
• What is the unit used for frequency?

  Hertz (Hz)
• What is meant by a frequency of 200Hz?

  200 waves pass a given point each second.
• What is wave speed?

  The speed at which energy is transferred through a medium
• What does a wave transfer?

  energy
• What is wave velocity?

  Wave velocity (measured in metres per second) is equal to the product of the wavelength and frequency of the wave.
• State the equation used to calculate wave speed. Give appropriate units.

  Wave Speed = Frequency x Wavelength

  Speed (m/s), Frequency (Hz), Wavelength (m)
• What is meant by the period of the wave?

  The length of time it takes for one full wave to pass through a point
• State the equation used to calculate wave speed. Give appropriate units.

  Wave Speed = Frequency x Wavelength

  Speed (m/s), Frequency (Hz), Wavelength (m)
• What word is used to describe when a wave bounces off a surface?

  reflection
• What is 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 (the angle it comes in at) is the same as the angle of reflection (the angle it leaves at).
• What is 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 (if it enters at an angle).
• 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 can refraction 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.
• What are the 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 do sound waves travel through a solid?

  The particles in the solid vibrate and transfer kinetic energy through the material.
• How does the human ear work?

  1. The outer ear collects the sound which travels into the ear

  2. The sound waves cause the eardrum to vibrate at the same frequency

  3. This is amplified by three ossicles (small bones)

  4. This causes the hair in the cochlea to vibrate

  5. The cochlea converts the vibrations into electrical signals

  6. The signals are passed to brain through the auditory nerve

  7. The brain converts the electrical signals into sound
• What is the frequency range of human hearing?

  20Hz-20kHz
• What is an ultrasound wave?

  A sound wave with a frequency greater than 20,000 Hz.
• What is sound frequencies less than 20Hz called?

  infrasound
• What natural event causes seismic waves to be produced? What types are produced?

  ● Earthquakes

  ● They produce both P-waves and

  S-waves
• Are P waves longitudinal or transverse?

  longitudinal
• Are S waves longitudinal or transverse?

  transverse
• State the difference between the mediums that P-waves and S-waves can travel through.

  ● P-waves travel through both solids and liquids

  ● S-waves only travel through solids (not liquids)
• What is the significance of P and S waves?

  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.
• What technique is used to detect objects in deep water and measure water depth?

  ● Echo sounding

  ● High frequency sound waves are emitted, reflected and detected

  ● Time difference between emission and detection, alongside wave speed, are used to calculate distances
• How does sonar work?

  ● When ultrasound waves are emitted they reflect off boundaries and their echoes are detected.

  ● The speed of the ultrasound is known and also the time it takes to detect the echoes.

  ● The equation distance=speed x time is used to find the distance travelled.

  ● The distance travelled is halved to give the distance between emitter and boundary (as the wave had to travel there and back.