Waves

• Waves


  Transfer energy without transferring matter
• Transverse waves


  • Cause the particles in the medium to vibrate at right angles to the direction of the waves motion
  • E.g. a cork in water or coils in a spring
  • Moves up and down as the wave passes
• Longitudinal waves


  • Cause a medium's particles to vibrate in the same direction as the waves motion
  • Sound waves are longitudinal waves
• Speed


  Frequency X Wavelength
• Amplitude


  The largest distance that a point on the wave moves from its rest position, the distance from the rest position to the top of the wave's peak
• Wavelength


  The distance between 2 adjacent wavefronts, for transverse waves this is the distance between two peaks
• Ripple tank practical


  1. Water waves can be set up in a ripple tank

  2. A rod at one end of a tank creates a series of ripples

  3. A bright light shone through the water onto a sheet of paper shows these ripples on the water in a set of parallel lines

  4. These are the waterfronts
• Waves at a boundary

  • The speed and wavelength change when it goes from one median to another, the speed and wavelength are directly proportional
  • The frequency is the same
• Absorption


  • Can happen at a boundary, this is where energy is absorbed by the material, such as a matt black surface
• Reflection


  • Happens when a wave hits a flat surface and bounces off
• Law of reflection


  Angle of incidence = angle of reflection
• Refraction of light


  • If light enters a new medium, this medium is less optically dense, this is refracted further from the normal, Making it larger than the angle of incidence
  • If it is denser then the light will be refracted closer to the normal
• Internal reflection


  • Light speeds up when entering a less dense medium, this causes some light to be refracted and reflected
• Electromagnetic waves


  • These are transverse and travel at the same speed in a vacuum
  • The speed is the same as the air in the vacuum
• Electromagnetic spectrum


  • There is a continuous spectrum of EM waves, EM waves transfer energy from the source of the wave to an absorber of the wave
  • This depends on two factors, the frequency and the length
• Wavelength vs frequency in EM waves

  • The wavelengths increase, and the frequencies decrease as you move down the radio waves, gamma to radio waves
  • Gamma rays have the shortest wavelength and highest frequency
• EM wave energy


  • Transferring energy from the source to the absorber of the wave
  • Gamma rays carry the most amount of energy
  • Wave energy increases with frequency
• Produce EM waves


  1. Electrical circuits - oscillations in circuits can produce radio waves

  2. Changes in atoms - changes in atoms and in their nuclei can result in EM waves being generated or absorbed, such as gamma rays
• Waveform


  How waves are presented, showing the amplitude, frequency, and wavelength
• Ripple tank


  This will tell measure the distance by ten peaks and divide by ten, also measure how long it takes, used to find out the waves in water
• Sound waves speed test


  Can be done through returning sound waves with an oscilloscope and calculate how long it takes to travel through echoes
• Sound and seismic waves

  • Sound waves cause the eardrum to vibrate, this notifies the brain
  • When it meets a boundary, some of the energy goes through but some is reflecting, this causes echoes and is used for ultrasound
• Electromagnetic spectrum


  • No medium to travel through, EM waves when electrons lose energy- absorbed by electrons, that's how they receive information or light
  • Gamma rays can make electrons leave their atoms and ionize them, can cause mutations
• Gamma rays


  • Carry the most energy out of all EM waves, they are used for medical imaging, astronomy, sterilization and food preservation
  • Risk of them is that they are damaging to living tissues and cells
• 1. rays


  • Carry the second most energy, low energy x rays are used for medical imaging and high energy ones are used to treat cancer, also for security detection
  • Danger is like gamma rays
• Ultraviolet light (UV)


  • Found between x-rays and visible light in the spectrum, used in medical and forensic photography, and used for forensics, air purification, disinfection and medical therapy
  • Too much exposure can cause skin burns and cancer
• Visible light


  • Found in the middle, we use this to see the world around us
  • We usually say that there are the seven colors in the rainbow that make up this spectrum
• Infrared radiation


  • Is after visible light, it is used in tv controls and body heat detectors in alarms
  • Can cause skin burns if emitted from high intensity sources
• Microwaves


  • Used in satellite communications, transmitting signals between mobile phones and vibrating water to cook food
  • Since humans are made up of water, exposure to microwaves could have harmful effects on people
• Radio waves


  • The lowest frequency in the spectrum, used for radio and tv communications
  • Can cause internal heating of living tissues at high intensity
• Visible light reflections


  • Diffuse reflection happens when light is reflected by a rough surface, scattering the light
  • A specular reflection is reflected by a smooth surface in a single direction
• Refraction


  • When waves enter a new medium, their speed and angle changes
  • The angle of refraction is smaller than the angle of incidence depending on how close it is to the normal
• Sound waves


  • These are longitudinal waves, they can travel through solids causing vibrations in the solid
  • Sound is produced by the vibration of particles in a medium, the vibrations mean that sound waves travel in a series of compressions (where the medium is squashed together) and rarefactions (where the medium is stretched apart)
• Ultrasound


  Has a frequency above 20,000 meaning humans can't hear it but animals can
• Speed of sound


  • Sound needs to travel through a medium, the more rigid it is the faster the speed of sound is through the medium
  • The more compressible it is, the slower it is
  • Solids are the fastest as they are hard to compress and more rigid than liquids
• Measuring speed of sound

  1. Echoes can be used to measure the speed of sound

  2. Two people can stand 100m from a tall vertical wall, the first person would make a sharp sound and repeat is every time an Echoe is heard

  3. The second person would measure the time taken for several claps

  4. The speed of sound can be calculated through (distance to wall X 2 X number of claps) / time taken for N claps
• Uses of sound waves

  • Sound waves can be transmitted, absorbed, reflected and refracted
  • This can be used for dog whistles, finding flaws in objects such as pipes
  • They can be used for ultrasound as they can see the reflected waves
  • We can see water depth from how long it takes for the wave to return from the surface
• Earthquakes


  • Seismic waves are waves that travel through the Earth
  • Earthquakes produce two types of seismic waves: P-waves (longitudinal) and S-waves (transverse)
• Use of seismic waves


  We can work out the different materials that Earth is made up off, we can detect seismic waves from earthquakes to find out that the Earth has a solid core surrounded by liquid outer core
• Concave lens


  • It is thin in the middle, thick on the top and bottom
  • When parallel rays enter the Lens, they disperse
  • If you trace back the rays, they all meet behind the Lens, this means the principal focus is behind the Lens
  • Also called diverging lens