reflection,refraction (refractive index)

reflection,refraction (refractive index)

1. changing of direction of light when it goes from one medium to another

   • when light crosses an interface ( a boundary between two transparent media of different densities ) it changes direction
     • no refraction occurs when the light eneters the interface at 90 degrees

2. reflection is when light strikes a reflective surface it changes direction.

   • for reflected light angles of incidence and reflection are the same

3. refractive index is the property of transparent media ----------- refractive index = sin i / sin r

   • refractive index for water - 1.0 ...air 1.33 and glass 1.5

4. converging lenses

   • or convex lenses are thickest at centre and represented by an double outward arrow in ray diagrams
   • pricipal focus is the point where the parrael light rays go through the lens and meet at one point
     • principle axis of the lens is a light ray that enters a lens at its centre is undeviated
   • Diverging lens
     • concave lens is the thinnest at the centre and represented by arrow heads facing inwards
     • when light rays hit the lens they diverge
     • diminished ... virtual and upright when image is on same side as object
     • shape of lens determined by its curvature ie how much a light ray is refracted through it
     • Focal length and lens power
       • power( dioptres )=1/focal length
         • concave lens always has negative answer
       • the focal length depends on the refractive index of the material of the lens and the curvature ( usually related to thickness of the lens ) of the surfcae
         • for a given focal length the greater the refractive index the flatter the lens..... the lens can be made thinner
       • The Eye
         • eye recieves light and sends this information to the brain via the optic nerve which interprets the image
         • cornea-refracts most of the light whilst the pupil ( opening the iris) adjusts the light intensity.
           • the lens provides futher refraction before the image is formed on the light-sensitive retina....the optic nerve carries this information to the brain
             • the ciliary muscles control the shape of the eye lens. this allows light from objects at different distances to be brought into focus
               • the eye can focus on objects between the near point - 25 cm and the far point - infinity
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   • focal length is the distance between the pricipal focus and the lens
   • image larger than object- virtual,upright and magnified
   • magnification is image height / object height
   • object futher away from principal focus- real,,inverted and diminished ( smaller )
   • if the image is formed by virtual light rays crossing the image is virtual.. HOWEVER if the image is on the same side as the object it is also virtual HOWEVER for the real image the image is on the opposite side of the lens and where real light rays cross