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P4 (Waves, Wave properties, Ray diagrams, Lenses, Electromagnetic…

- - - - Thus motion of particles is transverse (or perpendicular) to motion of wave and direction of energy flow
  - - - Amplitude also determines the volume of a sound wave
    - - In the diagram it is between two troughs, but could be equally be between two crests, or any two other corresponding points
    - - Also determines the pitch of a musical note
  - - - We can do this for any other crests in the wave, generating series of wavefronts
    - - Distance between each wave crest is the wave's wavelength (which is constant).
        
        Meaning distance between each wavefront must be constant and have same value as wave's wavelength
    - - If object causing waves to be formed is linear, they will appear linear and travel in straight lines
      - If object causing waves to be formed is spherical, then they will radiate out from object that makes them
  - - - velocity = frequency x wavelenggth
    - - Wavelength = velocity/frequency
  - - - As it moves forward, it pushes on closest air particle. This air particle in turn pushes on next and so on.
        
        Each individual particle is oscillating in place, but transfer energy to the next one, and so on along the line
- - - - Angle of incidence (i) - ray of light coming towards mirror, angle between incident ray and normal
      - Angle of reflection (r) - Angle between reflected ray and normal, ray of light which leaves the mirror after being reflected
      - These angles are measured from a line 90degrees to the boundary called the normal
  - - - Law of reflection still applies, can still draw a normal line perpendicular to the surface where the ray strikes it and determine the angle of reflection
      - As surface is irregular, normal line at each point on the surface will have a different angle.
        
        Each incident ray will reflect in a different direction, so light reflected will be spread out overall
  - - - Change in medium could involve light passing from air to glass, or water, or crystal- or going in the other direction
    - - When a wave changes medium, it will change speed and wavelength. but frequency remains the same
        
        When light changes mediums and slows down, it will bend towards the normal
        
        When light changes mediums and speeds up, it will bend away from the normal
    - - Light is scattered, scattering means light takes a lot longer to get where it needs to go
        
        Speed through medium is slower than speed of light
      - Denser media have more particles, so light scatters more and slows down more
      - Light travels fastest in a vacuum. There are no particles in a vacuum so light has a straight path from point to point
        
        Meaning there is nothing to scatter light and slow it down, allowing it to travel at the speed of light
    - - Normal
        
        Ordinary line that runs at 90 degrees to boundary of media. Usually represented with a dotted line
      - Angle between incident ray and normal is angle of incidence
      - Angle between refracted ray and normal is angle of refraction
    - - Measure how easily light can travel through different media
      - Denser medium - larger refractive index
        
        This means light ray bends towards normal when travels into medium with higher refractive index, and opposite with low refractive index
      - Vacuum has a refractive index of 1.00 (lowest possible index)
      - Calculate refractive index using angles
        
        n = sin i / sin r
        
        n = refractive index
        
        i = angle of incidence
        
        r = angle of refraction
    - - Ray of light has high enough angle of incidence, refracted ray will travel along boundary between two media
      - When the angle of incidence is equal to critical angle, it means angle of refraction = 90degrees
    - - When angle of incidence is larger than criticle angle, light won't be able to refract because there is no way for it to pass into the other substance
      - Can only occur when light travels into a medium with lower refractive index
        
        because light will bend away from normal
    - - Use total internal reflection to carry signals
      - Made out of glass fibers 10micrometres thick, designed so rays of light totally internally reflected back into glass.
        
        This way they can carry a signal over a long distance
      - Used for phone and internet cables, medical tech to observe regions of body difficult to reach
  - - - This results in a spread of circular waves
        
        Wave of diffracted wave is the same as before
      - If the gap that the wave passes through is larger than the wavelength nothing happens
        
        The waves continue in a straight line but may show bending at edges
  - - - This allows for radio and TV signals to be detected in hilly areas but do not have the same effects on waves which have smaller wavelengths
        
        Large wavelength = diffract more
  - - - Light we see can exist in the middle of this spectrum; because we can see it, it is referred to as visible light
      - Other types : Infrared, microwaves, radio waves, ultraviolet, x-rays and gamma rays
    - - When light moves through a medium the energy vibrates at right angles to the direction it travels in
        
        Light and other EMR waves are transverse ways.
      - Light travels with a velocity, and has a frequency and wavelength
        
        Light doesn't need a medium
        
        which is why light from the sun can travel through space to reach the earth
      - Wiggles up and down (or back and forth) as it moves forwards
    - - Travels at 3.0 x 10^8 m/s in a vacuum (basically 300,000km/s)
      - Speed limit of the universe, impossible for anything to travel faster than the speed of light
      - Light has a very short wavelength
    - - longest wavelengths (1mm - 100km)
      - Lowest frequency and least energy of all forms of emr
    - - Light waves of different frequencies and wavelengths
      - Lowest wavelength and frequency color is red
    - - Between visible light and x-rays
      - Produced by hot objects like the sun or solariums
      - Short wavelengths ranging 10-400nm
      - High frequencies and high energy
      - UV travels through the atmosphere with infrared radiation (felt as heat) and visible light (what we see)
      - UV exposure is important as it helps produce vitamin D, which is needed to absorb calcium and fight infections and bone growth
        
        Exessive uv exposure can cause skin damage, eye damage and skin cancer
        
        UV radiation is able to deactivate bacteria + viruses
    - - Sits between UV and gamma rays
      - Short wavelength ranging 0.01nm to 10nm
      - High frequency and high energy level
      - Density of medium determines how many x-rays can pass through it
      - Commonly used for medical imaging because they can pass through low density tissue like muscle
        
        But is absorbed or scattered by high density tissue like bone
      - Long term exposure to x-rays can damage cells. can cause mutations which lead to cancer
- - - - Trace the rays backwards behind the lens to find point where they do appear to cross
    - - Principal axis is line that runs directly through center of lens
      - Where object is placed
      - Important reference for rays that will be drawing
    - - First ray
        
        travels parallel to principal axis and passes through principal focus on the other side of len
      - Second ray
        
        Goes from object straight through centre of lens without refracting
      - Third ray
        
        Travels through principal focus closest to object and travels parallel to principal axis on the other side of lens
      - When the three rays are combined onto a single diagram, an image is formed where the light rays cross
  - - - Real image is formed when light rays actually cross
      - Virtual image is formed when the rays only appear to cross
        
        Formed when diverging rays are traced back to where they appear to cross - mirrors are virtual images
    - - Enlarged image - bigger than the object
      - Diminished image - smaller than the object
      - Longer image arrow on diagram = larger object
    - - Image is upright if image arrow points up
      - Inverted if the image is pointing down, meaning it is upside down
  - - - First ray acts the same
      - Second ray goes straight from object through center of lens
      - Third ray goes through focus on object's side of lens, then goes parallel to principal axis
  - - - Determine the angle by tracing it backwards
- - - - Lenses make light change direction- this shrinks or magnifies an image
    - - Convex
        
        Bulges out in the middle
        
        Found in glasses and cameras
        
        Example: magnifying glass
        
        When you hold a magnifying glass in front of an object, we see an enlarged image
        
        Causes parallel light rays to converge, meaning rays meet and form an image
      - Concave
        
        Cause parallel light rays to diverge. meaning they move apart and do not cross. You still see an image with concave lenses
        
        Curved inwards in the middle
        
        Used in flash lights, telescopes, binoculars
        
        Example of concave: glasses
        
        Short sightedness - Light entering your eye will focus in front of retina, due to a long eyeball or inability of lens in your eye to focus correctly
        
        Short sightedness is corrected using glasses containing concave lenses, which focus light on your retina resulting in forming sharp images
      - All lenses have principal focus and length
        
        Principal focus - point where light rays converge (or appear to diverge form) after passing through lens
        
        Focal length - distance between either principal focus and centre of lens