Waveslay

• Waves - transfer energy from one place to another, yet they don’t transfer any matter.

  To transfer from one place to another, the waves vibrate or oscillate.
• On a graph..

  Top part of the wave: crest

  Bottom part of the wave: trough
• Frequency = 1/time

  (frequency is measured in Hz, and is the number of complete oscillations per second)
• Wave speed (m/s) = frequency (hz) x wavelength (m)
• Transverse Wave - Oscillations are perpendicular to the direction of the energy transfer.

  E.g light and radio waves
• Waves aren’t always reflected, three things may happen:

  • The wave might be absorbed by the material 
  • The could be transmitted, where it hits the material but carries on travelling (it passes out the other side) , it 

  often leads to refraction 

  • The wave could be reflected off the surface 
• Longitudinal Wave - Oscillations are parallel to the direction of the energy transfer.This causes some regions (on the graph) to be more spread out and others to be more compressed, this is because the waves are vibrating back and forth.

  E.g sound waves 
• Ray diagrams:

   Angle of incidence = angle of reflection 

  1. Drw incoming ray and label with an arrow of direction 
  2. Draw the ‘normal’ with a dotted line, this is perpendicular to the boundary 
  3. Measure angle of incidence, the angle of reflection must be the same as the angle of incidence 
  4. Draw angle of reflection from the boundary, and label with an arrow of direction
• Specular Reflection: the boundary is flat, so the normals are in the same direction. This gives a clear image.
• Diffused/scattered reflection: the boundary is bumpy, so the normals will all be in different directions. This means light will be reflected in different directions.
• Refraction of light waves = when waves change direction as they pass from one medium to another.
• Waves travel at different speeds in different materials (mediums), this is because they have different densities. 

  The more dense the medium, the slower a wave will travel through it. 
• A wave will travel at an angle towards the medium, when it reaches the medium it’ll refract closer towards the normal. 
• Ray Diagrams for Refraction:

  1. Draw the normal at the point of incidence (where the incident ray meets the surface)
  2. If the medium is more dense the medium its currently in (air), you need to draw the refracted ray from the point of incidence, but closer to the normal 
  3. Label angle of incidence and angle of refraction 
• The speed of the wave is changing as it passes from one medium to another. 

  Wave speed = frequency x wavelength

  Frequency always stays the same if the speed of the wave changes, so the wavelength changes. 
• Different wavelengths are refracted by different amounts.(think pink floyd album cover)
• Electromagnetic waves are ALL transverse waves, so they oscillate perpendicular to the direction of the energy transfer. In a vacuum, they’ll travel at the same speed of 3x10^8 m/s.However in different mediums, they travel at different speeds. 
• In the electromagnetic spectrum, wavelength and frequency are inversely related. 

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• Visible Light:

  • Only part of the spectrum human eyes can detect
  • Their different wavelengths give you the different colours 
• Electromagnetic spectrum:

  • Radio waves 
  • Micro waves
  • Infrared waves
  • Visible light 
  • Ultra violet 
  • X rays
  • Gamma rays 
• Ultra violet, x and gamma rays are ionising and cause damage to our cells.

  Radio and Micro waves are used in communication.
• Where the waves come from:

  • Infrared = bonds that hold molecules together vibrate
  • Visible light, ultraviolet + x rays = when electrons drop down energy levels 
  • Gamma rays = radioactive decay 
• Once emitted, all the waves can travel across the universe and empty space. When they come in contact with something, they can be either reflected, absorbed or transmitted. 
• Radio Waves:

  • Longest wavelength 
  • Lowest frequency 
• How to produce radio waves:

  1. Use a transmitter (normally connected to an oscilloscope which allows you to see the frequency of the alternating current)
  2. Once the radio wave has been generated, detect it again by using a receiver, which absorbs the energy and creates an alternating current and is displayed on a different oscilloscope 

  The frequency of the alternating current produced is exactly the same as the frequency used to generate the radio wave in the first place.
• Radio Waves For Communication:

  1. Long waves = transmitted over huge distances (e.g from london to Singapore) without having to interact with anything along the way. This because the diffract (bend) around the curved surface of the earth 
  2. Short waves = transmitted over long distances but cannot bend around the earth, they’re reflected from the ionosphere. Can send short distances too, like the bluetooth in your phone 
  3. Very short waves = used for tv and fm radio, they travel directly from the transmitter to the reciever 
• Ionosphere = electrically charged layer of the  upper atmosphere 
• Infrared waves:

  • Long wavelengths 
  • Low frequencies 
• Infrared radiation = emitted from all objects that have thermal energy (dependent on temperature)
• Uses of infrared radiation:

  • Infrared cameras help you see in the dark and help spot living organism - animals that are warmer because they emit more infrared radiation 
  • Cooking by heating metals to very high temperatures in ovens and grills. This allows you to emit lots of infrared radiation(without penetrating the surface) which heats the food by transferring thermal energy 
  • Electric heaters, thy use electrical energy to heat metal of the heater which emits infrared radiation to the surroundings and heat up rooms 
• Microwaves and infrared waves are only harmful in high quantities. Background radiation doesn’t do you any harm.
• Microwaves that are not absorb by water molecules:

  • Used for communication using satellites, which means the microwaves have to pass through the earth’s atmosphere. Then they’re received by a satellite and transmitted back down to earth where satellite dishes detect them
• Microwaves that are absorbed by water molecules:

  • Used in microwave ovens where they help heat food up. This is because most of the food we eat contains lots of  water molecules 
  • When the microwaves are fired at the food, the energy from the waves gets absorbed by all the water molecules as they start to vibrate more, they transfer energy to neighbouring molecules so that it spreads throughout the food via conduction/convection 
• Visible light can be used for communication using optical fibres. They’re thin plastic/thin glass fibres (materials that totally reflect light + have specular reflection) that are able to transmit pulses of light over long distances because the light is reflected every time it hits the surface until it can be interpreted. 

  This allows you to transmit data really quickly 
• Visible Light = the light you use to see and have different colours depending on its wavelength. For example, red has the longest and violet has the shortest wavelength 
• An alternative to using thin glass/plastic is with copper wires and electricity but they don’t transmit as much information and signals are more likely to be distorted during transmission
• Ultraviolet radiation:

  • Has shorter wavelength than visible light 
  • E.g sun rays can tan/burn you 
• Fluorescence = a property of certain chemicals where ultraviolet light is absorbed and then the energy is re-emitted as visible light.
• Fluorescent Lights: energy efficient 

  • Generate ultraviolet radiation 
  • That radiation is absorbed by a layer of phosphorus that coats the inside of the bulb 
  • Re-emits the energy as visible light 
• Ultraviolet and Security: security pens appear completely invisible until you shine you a ultraviolet light on it