Chapter 11

• Displacement is the distance from the equilibrium position in a particular direction
• amplitude is the maximum displacement from the equilibrium position
• wavelength is the minimum distance between two points in phase on adjacent waves
• period is the time taken for one oscillation or time taken for one wavelength past a given point
• wave speed is the distance travelled by the wave per unit time
• wave speed is the distance travelled by the wave per unit time


  $v=$$f\lambda$
• frequency is the number of wavelengths passing a given point per unit time


  $f=$$\frac{1}{T}$
• Phase difference is the difference between the displacements of particles along a wave or different waves
• An oscilloscope can be used to determine frequency. The vertical scale is the voltage and the horizontal scale is the time.
• Reflection occurs when a wave changes direction at a boundary between two different media, remaining in the original medium
• The law of reflection states that the angle of incidence is equal to the angle of reflection.
• Refraction occurs when a wave changes direction as it changes speed when it passes from one medium to another.
• If a wave enters a more dense medium, the wave slows down and refracts towards the normal
• If a wave enters a less dense medium, the wave speeds up and refracts away from the normal
• Diffraction is the spreading out of waves as they pass through a narrow opening.
• Polarisation is where a wave is confined to a single plane, so it can only oscillate in one direction.
• The intensity of a wave is defined as the radiant power passing through a surface per unit area.


  $I=$$\frac{P}{A}$
• Intensity has an inverse square relationship with the distance from the source


  $I\propto\frac{1}{r^2}$
• Intensity is directly proportional to the square of amplitude


  $I\propto A^2$
• Radio waves are used to transmit information and are used in wireless communication. They have the lowest energy and have a wavelength between $>10^6 m - 10^{-1}m$
• Microwaves are used for cooking food, satellite communication, and medical imaging. They have a wavelength of $10^{-1}m - 10^{-3}m$
• Infrared radiation is used in electrical heaters, short-range communications like remote controls and thermal imaging cameras. They have wavelengths of $10^{-3}m - 7\times10^{-7}m$
• Visible light is used in photography and illumination: this is the type of light we can see. They have wavelengths of $7\times10^{-7}m-4\times10^{-7}m$
• Ultraviolet rays are used in tanning beds and sterilization. They have wavelengths of $4\times10^{-7}m - 10^{-9}m$
• X-rays are used to diagnose and treat diseases, such as cancer through internal imaging. They have wavelengths of $10^{-8}m-10^{-13}m$
• Gamma rays are used for sterilising food and medical instruments in the treatment and detection of cancer. They have wavelengths of $10^{-10}m-<10^{-16}m$
• The wave speed equations for EM waves is

  $c=$$f\lambda$
• The angle at which light is refracted depends on the refractive index of the material.


  $n=$$\frac{c}{v}$
• Snell's law


  $n_1\sin\theta_1=$$n_2\sin\theta_2$
• Total internal reflection occurs when the light is travels into a material with a lower refractive index than the one it is already in and the angle of incidence is greater than the critical angle.
• Total internal reflection occurs when the light is travels into a material with a lower refractive index than the one it is already in and the angle of incidence is greater than the critical angle.


  $\sin C=$$\frac{1}{n}$
• An optical fibres use total internal refraction to reflect light through them. A fine glass core is surrounded by glass cladding with a lower refractive index containing the light within the core.