Waves

• Transverse Wave


  A wave whose vibration is perpendicular to the direction of energy transfer

  
• Longitudinal Wave


  A wave whose vibration is parallel to the direction of energy transfer

  
• Examples of Transverse Waves


  Light
• Examples of Longitudinal Waves


  Sound
• Amplitude


  The distance between the peak and equilibrium line

  
• Wavefront


  An imaginary surface that we draw to represent the vibrating part of a wave.
• Frequency


  The number of complete waves/oscillations per second, measured in Hertz
• Wavelength


  The distance between two consecutive peaks, symbol is a lambda

  
• Time Period


  The time taken for one complete wave to pass a fixed point
• Waves


  The transfer of energy and information without transferring matter
• Reflection


  When light hits a smooth surface and bounces off of it

  
• Refraction


  When light changes speed when entering a different density medium, causing it to change direction

  
• Total Internal Reflection


  When light hits a boundary to a less dense medium at an incident angle greater than the critical angle, it reflects

  
• What is the critical angle (c)?


  * The angle where the angle of incidence is greater than 90.

  * The ray changes from just refracting to total internal reflection.
• Conditions Required for Total Internal Reflection to occur


  * Light starts in a more dense medium and tries to escape to a less dense medium.

  * The incident angle is greater than the critical angle
• Doppler Effect


  * The observed change in frequency of a wave.

  * This is due to the relative motion of the source and the observer.

  * As the velocity is the same, the frequency increases/decreases, so the wavelength increases/decreases
• Electromagnetic Spectrum


  * Gamma rays have the smallest wavelength.

  * Radio waves have the biggest wavelength.

  * Gamma waves have the highest frequency.

  * Radio waves have the smallest frequency.
• What speed do the waves of the EM spectrum travel in free space?


  They all travel at the same speed in free space
• Radio Waves


  * Radio

  * Television

  * Communications (walkie-talkies)
• Microwaves


  * Heating food

  * Satellite communication
• Infarared Radiation


  * Heat treatment for illness

  * Night vision

  * Remote control
• Visible Light


  Red, orange, yellow, green blue, indigo violet - vision and optical fibres
• Ultra-violet


  * Tanning beds

  * Killing bacteria

  * Forgery detection
• X-Rays


  * Medical imaging

  * Seeing hidden bombs (security)
• Gamma Rays


  * Killing cancer cells (radiotherapy)

  * Sterilising equipment
• Dangers of Radio Waves


  Can cause a very small rise in temperature of up to 0.2C. Otherwise nothing.
• Dangers of Microwaves


  Can cause internal heating of body tissues
• Dangers of Infrared Radiation


  Can cause skin to burn
• Visible Light Dangers


  A very intense laser can damage the retina of the eye; blindness
• Ultraviolet Dangers


  Can damage skin surface cells, leading to skin cancer; blindness
• Dangers of X-Rays


  Damages cells inside the body by causing dangerous ionisation. This leads to cancer.
• Dangers of Gamma Rays


  Damages cells inside the body, causing dangerous ionisation in living cells which damages DNA. Can lead to death, cancer or mutation
• Uses of Radio Waves


  Broadcasting and communications
• Uses of Microwaves


  Cooking and satellite transmissions
• Uses of Infrared Radiation


  Heaters and night vision equipment
• Uses of Visible Light


  Optical fibres and photography
• Uses of Ultraviolet


  Fluorescent lamps
• Uses of X-Rays


  Observing internal structure of objects and materials, including for medicial applications
• Uses of Gamma Waves


  Sterilising food and medical equipment
• Which end of the EM spectrum has the lowest wavelength?


  Gamma-Radio