3. Waves

• wavelength is the distance on a wave between two crests or troughs
• amplitude is the height of a sound wave or the depth of a trough. this corresponds to how loud a sound is
• frequency is the number of waves passing one point per second. this corresponds to the pitch of the sound
• the angle of incidence is the angle between an incident ray and the normal to the surface point where is meets the surface
• the angle of reflection is the angle between a reflected ray and the normal to the surface at the point where is meets the surface
• the angle of refraction is the angle between a refracted ray and the normal to the surface at the point where is passes from one material to another
• an axis is the line passing through the centre of the lens, perpendicular to its surface
• a compression is a region of a sound wave where the particles are pushed close together
• the critical angle is the minimum angle of incidence at which total internal reflection occurs
• diffraction is when a wave spreads out as it travels through a gap or past the edge of an object
• dispersion is the separation of different wavelengths of light because they are refracted though different angles
• transverse waves are waves that vibrate or oscillate perpendicular to the direction of energy transfer
• transverse waves transfer energy, but not the particles of the medium, they can move in solids and on the surfaces of liquids but not inside liquids or gases. some transverse waves (electromagnetic waves) can move in solids, liquids and gases and in a vacuum
• longitudinal waves are waves where the points along its length vibrate parallel to the direction of energy transfer
• longitudinal waves transfer energy, but not the particles of the medium, they can move in solids, liquids and gases. they can not move in a vacuum (since there are no particles)
• Close together, called compressions
• Spaced apart, called rarefactions
• the doppler effect is the apparent change in wavelength and frequency of a wave emitted by a moving source
• the doppler effect can be observed as the frequency of the sound waves emitted by ambulance or police sirens goes from a high pitch to a low pitch as the vehicle whizzes past
• the doppler effect can be observed as galaxies in outer space emit electromagnetic radiation - light waves - which appear to be redder than normal because the stars are moving away from us
• if the object emitting waves begins to move, the waves can get squashed together at one end of the object, and stretched at the other end
• The waves at the front of the moving vehicle appear to be squashed together, this means the wavelength decreases (and the frequency of the waves increases)
• The waves behind the moving vehicle appear to be stretched out, this means the wavelength increases (and the frequency of the waves decreases)
• Electromagnetic waves are defined as transverse waves that transfer energy from the source of the waves to an absorber
• All electromagnetic waves share the following properties, they are all transverse, they can all travel through a vacuum, they all travel at the same speed in a vacuum
• there are 7 types of electromagnetic waves, which all together form a continuous spectrum
• The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies
• Visible light is the only part of the spectrum detectable by the human eye. However, it only takes up 0.0035% of the whole electromagnetic spectrum. In the natural world, many animals, such as birds, bees and certain fish, are able to perceive beyond visible light and can see infra-red and UV wavelengths of light
• Visible light is defined as the range of wavelengths which are visible to humans
• Each colour within the visible light spectrum corresponds to a narrow band of wavelength and frequency
• The different colours of waves correspond to different wavelengths, red has the longest wavelength (and the lowest frequency and energy) and violet has the shortest wavelength (and the highest frequency and energy
• Wavelength and frequency are inversely proportional, this means that an increase in wavelength is a decrease in frequency (towards the red end of the spectrum). A decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)
• radio waves are used for communication e.g. radio and TV
• microwaves are used for heating food and communication e.g. Wifi, mobile phones and satellites
• infrared waves are used for remote controls, night vision goggles, infrared cameras and heating and cooking things
• visible light waves are used for seeing and taking photographs (videos) and fibre optic communications
• ultraviolet waves are used for fluorescence (security marking), fluorescent light bulbs and getting a suntan
• x-rays are used for x-ray machines
• gamma rays are used for sterilizing medical instruments and treating cancer
• As the frequency of electromagnetic (EM) waves increases, so does the energy, beyond the visible part of the spectrum, the energy becomes large enough to ionise atoms