Waves and Optics

• Created by: Sagaana
• Created on: 29-12-18 10:41
• Waves and Optics
• wave
• Waves and Vibrations
• transverse waves - directions of the waves is perpendicular to the vibration of the particles
• Longitudinal waves- the direction of the wave is parallel to the vibration of the particles.
• Waves are plane polarised if the vibration stay in the one plane only,
• what is the test that helps us distinguish transverse waves  from longitudinal waves.
• Untitled
• measuring waves
• amplitude-it is the maximum displacement of an oscillating particles
• Wavelength- it the distance between two crest or two trough
• period= 1 / f
• Wave properties
• Waves change speed when they pass across the boundary causing them to bend
• When light goes thru glass from air they bend toward the normal. and then they go from glass to air they will bend away from the normal.
• diffraction occurs when the waves spread out after passing thru a gap around an obstacle
• when two start at the the same point they superpose to produce a reinforcement = addition
• When two waves start at a different point when they superpose they cancel out = cancellation
• Total cancellation is rarely achieved in practice because 2 waves are unlikely to have the exactly the same amplitude and wavelength.
• Stationary and Progressive waves
• Stationary waves can be produced. when a wave with correct wavelength meets it reflection the interference of the two waves produces a resultant wave that doesn't appear to move
• stationary waves are formed by superposition as when the two waves are in phase with each other they reinforce and when the two waves have moved they cancel each other out
• Nodes are formed because they are region in a vibration wavelength with no energy likely caused by destructive interference
• More on stationary waves on a string
• What condition must the be satisfied at both ends a a string ?
• The first Harmonic pattern vibration is seen at the lowest possible frequency this has the anti-node at the middle  and the nodes at the end. the length of the node 1/2 lambda
• Compare the frequency of the first harmonic and the last harmonic?
• Using an Oscilloscope
• Optics
• Reflection of light
• ray-it is a line that is perpendicular to the lights wave fronts ,
• Snell's Law- Sin i /Sin r      it is also know as the refractive index.
• Refraction and light travelling from transparent system substance into air  is the same thing as refraction is parallel  however ti would be different if the transparent substance is a triangular prism.
• More about refraction
• when light enters water from air the speed of water changes.The speed of light slows down.
• when the incident angle is greater than the refractive angle the speed of light slows down.
• When the incident angle is smaller than the refractive angle the speed of light speeds up.
• light disperse when it enter a glass prism because light is made up many wave length the glass prism refracts light  by different amounts depending on the wavelength so the refractive index of light is greater than the refractive index of red light.
• Total internal reflection
• for total internal reflection to take place the incident substance must have a larger refractive index than the other substance and the angles of incidence exceeded the critical angles
• The refractive index and the critical angle are related through snells law
• Diamonds sparkle because when white light enter the diamond it it the split into colours of the spectrum and diamonds have a very high refractive index of 2.417 so it separates the colours more than any other substance so it refracted many time before emerges.
• Double slit expriment
• The source of waves must be coherent and they must be mono-chromatic
• light is being shone through a pair of vertical slits and it is diffracted into a pattern on the screen with numerous vertical lines spread horizontally
• the amplitude of the waves add and pure constructive interference is obtained when identical waves are in phase and destructive waves are out of phase
• to increase the fringe space t you will need to increase the distance from the slit and screen the wavelength used will also needed to be increased and the split spacing used must be decreased  you will need to do the opposite to decrease the fringe spacing.
• Interference
• coherent sources are when they emits waves with constant phase difference
• if two lights ere used it would not form a interference pattern because the two lights sources emit light waves randomly so the point of interference and cancellation would change at random so no interference pattern would be possible.
• interference and diffraction in  young's fringes ?
• Diffraction
• In Microscopes they use blue filter as it gives a higher resolution because blue is refracted more than any other colour.and therefore electrons are diffracted less as they pass through the microscope magnetic lenses
• the single slit experiment meant that when light did refract it would make a pattern on the screen.This pattern is made of bright spots and faint spots. The brightest spot was the central maxima and the the further fringes are more faint the more further away it is from the central maxima
• in the single slit experiment the spot are much larger ans more spread out. however with double slit the width of the fringes would be the same.
• Diffraction grating
• Diffraction grating diffracts monochromatic light in certain direction because the light passing through each slit is diffracted  and the diffracted light waves from adjacent slits reinforce and cancel out in other in all other directions.
• coarse grating?