waves

• waves carry energy from one place to another and can also carrry information
• waves are either transverse or longitudinal waves depending on the direction of the oscilllations
• an example of a transverse wave the ripple on a water surface
• longitudinal waves show areas of compression and rarefaction
• sound waves travelling through air are longitudinal waves
• a longitudinal wave is a wave which the oscillations are parallel to the direction of energy transfer
• a transverse wave is a wave that oscillates perpendicular to the direction of the wave
• the difference between a longitudinal and a transverse wave is that a longitudinal wave travells parallel to the direction of the wave and a transverse waves travels perpendiular to the direction of the wave
• Amplitude - the amplitude of a wave is the maximum displacement of a point on a wave from its undisturbed position
• Wavelength - the wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave
• Frequency - the frequency of a wave is the number of waves passing a point each second
• What is the formula to calculate the period of a wave

  
• The units for time is seconds and the units for frequency is hertz
• What is the formula to calculate wave speed

  Wave speed = frequency × wavelength
• the unit for wave speed is m/s
• the unit for wavelength is in meters
• when describing a method to measure the sound waves in air involves using a resonance tube apparatus. by placing the tube horrizontally through a tank of water and adjusting the water level, resonance can be achieved. the length of the air collumn is then measured, and through calculations involving frequency and wavelength, the speed of sound can be determined
• the apparatus needed for the resonance tube practical is a resonance tube, water tank,tuning fork, ruler or measurig tape,and a thermometer
• to measure the speed of ripples on a water surface you can use a ruler to mark a fixed distance and then time how long it takes for a ripple to travel that distance. by repeating the process and averaging the times, you can calculate the speed of the ripples using the equation speed = distance/time
• when sound waves pass from one medium to another, their velocity changes due to the different properties of the mediums. however, the frequency remains constant, while the wavelength changes to maintain the realtionship: velocity=frequency * wavelength. this relationshipshows how changs in velocity, frequency, and wavelengthare inter-related
• waves can be reflected at the boundary between two different materials
• waves can be absorbed or transmitted at the boundary between two different materials
• Conversion of sound waves to vibrations in solids

  1. Sound waves cause the ear drum and other parts to vibrate

  2. Causes the sensation of sound
• The conversion of sound waves to vibrations of solids works over a limited frequency range
• This restricts the limits of human hearing
• Students should be able to

  • Describe, with examples, processes which convert wave disturbances between sound waves and vibrations in solids
  • Explain why such processes only work over a limited frequency range and the relevance of this to human hearing
• The range of normal human hearing is from 20 Hz to 20 kHz
• Differences in velocity, absorption and reflection between different types of wave in solids and liquids

  • Can be used for detection and exploration of structures hidden from direct observation
• Ultrasound waves

  Waves with a frequency higher than the upper limit of hearing for humans
• Use of ultrasound waves for imaging

  1. Partially reflected when they meet a boundary between two different media

  2. Time taken for reflections to reach a detector used to determine distance to boundary

  3. Allows ultrasound waves to be used for medical and industrial imaging
• Seismic waves

  • P-waves are longitudinal, travel at different speeds through solids and liquids
  • S-waves are transverse, cannot travel through a liquid
  • P-waves and S-waves provide evidence for the structure and size of the Earth's core
• Echo sounding

  Uses high frequency sound waves to detect objects in deep water and measure water depth
• The study of seismic waves provided new evidence that led to discoveries about parts of the Earth which are not directly observable
• Electromagnetic waves

  Transverse waves that transfer energy from the source of the waves to an absorber
• Electromagnetic waves form a continuous spectrum and all types travel at the same velocity through a vacuum (space) or air
• Groups of electromagnetic waves

  • Radio
  • Microwave
  • Infrared
  • Visible light (red to violet)
  • Ultraviolet
  • X-rays
  • Gamma rays
• Our eyes only detect visible light and so detect a limited range of electromagnetic waves
• Different substances may absorb, transmit, refract or reflect electromagnetic waves in ways that vary with wavelength
• Refraction is due to the difference in velocity of the waves in different substances
• Constructing ray diagrams to illustrate refraction

  Illustrate the refraction of a wave at the boundary between two different media