electromagnitism

• Waves


  Carry energy from one place to another and can also carry information
• Waves


  • Common in both natural and man-made systems
• Designing comfortable and safe structures such as bridges, houses and music performance halls requires an understanding of mechanical waves
• Modern technologies such as imaging and communication systems show how we can make the most of electromagnetic waves
• Transverse waves


  Waves where the oscillation is perpendicular to the direction of energy transfer
• Longitudinal waves


  Waves where the oscillation is parallel to the direction of energy transfer
• Transverse waves


  • Ripples on a water surface
• Longitudinal waves


  • Sound waves travelling through air
• For both ripples on a water surface and sound waves in air, it is the wave and not the water or air itself that travels
• Amplitude


  The maximum displacement of a point on a wave away from its undisturbed position
• Wavelength


  The distance from a point on one wave to the equivalent point on the adjacent wave
• Frequency


  The number of waves passing a point each second
• Period


  The time for one wave to pass a given point
• All waves obey the wave equation: wave speed = frequency x wavelength
• Students should be able to apply the wave equation: wave speed = frequency x wavelength
• Measuring wave properties


  1. Identify amplitude and wavelength from diagrams

  2. Measure speed of sound waves in air

  3. Measure speed of ripples on a water surface
• Changes in velocity, frequency and wavelength, in transmission of sound waves from one medium to another, are inter-related
• Reflection of waves


  Waves can be reflected at the boundary between two different materials
• Transmission and absorption of waves


  Waves can be absorbed or transmitted at the boundary between two different materials
• Constructing ray diagrams


  To illustrate the reflection of a wave at a surface
• Students should be able to describe the effects of reflection, transmission and absorption of waves at material interfaces
• Sound waves can travel through solids causing vibrations in the solid
• Within the ear, sound waves cause the ear drum and other parts to vibrate which causes the sensation of sound
• The conversion of sound waves to vibrations of solids works over a limited frequency range, which restricts the limits of 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 both for detection and exploration of structures which are hidden from direct observation
• Ultrasound waves


  Waves with a frequency higher than the upper limit of human hearing
• Ultrasound waves are partially reflected when they meet a boundary between two different media, allowing the time taken for the reflections to reach a detector to be used to determine how far away such a boundary is
• Seismic waves are produced by earthquakes, with P-waves being longitudinal and travelling at different speeds through solids and liquids, and S-waves being transverse and unable to travel through liquids
• 1. waves and S-waves provide evidence for the structure and size of the Earth's core
• Echo sounding, using high frequency sound waves, is used 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 the refraction of a wave at the boundary between two different media
• Using wave front diagrams

  To explain refraction in terms of the change of speed that happens when a wave travels from one medium to a different medium