Waves Flashcards
Waves
Transfer of energy through a medium caused by oscillation or vibration
-energy is tranferred not matter
Longitudinal waves
- medium oscillates parallel to the direction of energy travel
- caused by compressions and rarefactions of same medium
- cant travel in vacuum as particals are needed so change of density
- eg. Sound, mechanical waves (slinky/spring), deep water waves, earthquakes, AC
Transverse waves
- field oscillates perpendicular to direction of energy transfer
- caused by vibrations of field/medium
- density is constant
- can travel through medium
- light, em waves,ripples on water
Human ear range- sound waves
20HZ-KHz
What is amplitude in sound measured in
Decibels
Ultrasound
- frequency above 20khz
- used in sonograms(pregnany scans), echolocation, cleaning
Infrasound
-sound below 20Hz
Dangers of sound
- xtremely loud sounds- extreme pressure changes- force on eardrum bsting it
- exposure to loud sounds over long time- damage
How to prevent danger of sounds
- ear protection
- shorter time w/ loud sounds
- positioning behind sound
Refraction
Wave changes direction due to change in soeed at boundry
-depends on refractive index
Plano
Flat one side
Double
Both sides
Convex
Wider middle
Concave
Smaller in middle
Focal point
Point at which parallel light rays (which have passed through a lens) converge
- determined by shape and material of len
- sharp images formed at focal point
Converging rays
-light rays focus on one point
Diverging rays
-spread out as if from one point
Frequency
How many waves pass a point per second
Time period
How ong it takes for one complete osciallation or cycle
Wavelength
Distance two neighboring peaks
Amplitude
-maximum displacement of the vibration from rest
High pitch
- higher frequency
- same heught amplitude
Higher volume
Higher amplitude
Same wavelength and frequency
As wave speed increases
Bends away from normal
What happens when a wave is absorbed
- wave stops travelling
- goes into but not through medium
- energy is transferred to the material, causing the material’s energy store to increase
- kinetic store- moves
- internal energy stores-heat up or change state
- chemical energy store- light waves photosynthesis
Wave is transmitted
Wave continues moving through medium
- wave may be changed- diffraction and rfraction
- eg. Light through glass, sound through air
Diffaction
- waves spread out when passes through gap or round corner
- narrower the gap/greater the wavelength- more the diffraction
- only occurs if the gapsize is approx same as wavelength
- wavelength, frequency and speed unchanged
TIR
Total internal reflection
- greater than critical angle- light reflects beack into medium
- light must be traveling from a more optically dense medium into less optically dense medium (glass to air)
At critical angle
- emergent ray is perpendicular to normal
- moves along boundry
Optical fibres
- long thin rod of glass
- uses tir to transfer info by llight
- used medicine-endoscopy
- communications- high speed data transfer
Positives of optical fibres
- high bandwidth-lots info per second
- cheaper than copper
- long distances without losses
Negatives optical fibres
- complex
- more fragile
Telecoms- optical fibres
- info sent at speed of light through binary code (turning light on and off)
- interpreted by computer
Endoscopy- optical fibres
- doctors use so can diagnose or surgery
- light shone one end- tir
- light reflects back into another fibre- taking info up to camera so doctor can see
Dispertion
- seperating of diff wavelengths (colours) of white light upon reraction through a glass prism
- roygbiv from top (red at top, violet at bottom)
Greater wavelength
- slower the speed
- greater refractive index
