*Refraction 1Copyright Mark JordanDavitt College,CastlebarFor non-commercial purposes only.. Enjoy!Comments/suggestions please to the SLSS physics website forum@http://physics.slss.ie/forum

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*GlassAirirRay of light travelling from less dense medium (e.g. air) to more dense medium (e.g. glass) changes direction or bends called Refraction. A normal (90o) to point where the light enters dense medium (glass) shows ray bending into the normal.Incident rayRefracted rayAngle of refractionAngle of incidenceNormalRefraction

*RefractionGlassAirLight ray travelling from a more dense medium (glass) to a less dense medium (air) bends away from the normal - Snells Law again applies i.e. sin i sin rriWe can verify Snells Law with an ExperimentAngle of refractionAngle of incidenceNormalRefraction is the bending of a wave at the boundary when it is going from one medium to another

*Using a ray box and a block of glass record the values for the angle of incidence & angle of refraction as shown.

*Find the sine of angles of incidence and refraction and record Draw graph of sin i (y- axis) against sin r (x-axis)

i/ or / o35o23o40o26o45o29o50o32o55o34o60o36o65o38o

sin isin r0.570.390.640.440.70.490.760.530.810.560.860.590.900.62

*Choose coordinates on line Draw graph of sin i (y-axis) against sin r (x- axis)Refractive index (n) == 1.48Slope = k = n(0.68, 1.0)(0.14, 0.2)Straight line graph through the origin proves Snells Law i.e. Sin i Sin r

Chart1

0.57

0.64

0.7

0.76

0.81

0.86

0.9

Refractive Index

Sin r

Sin i

Sheet1

0.570.39

0.640.44

0.70.49

0.760.53

0.810.56

0.860.59

0.90.62

Sheet1

Refractive Index

Sin r

Sin i

Sheet2

Sheet3

*Waves going from air to glass at angle other than 90o velocity decreases frequency remains constant Wavelength decreases (from c = f )

*iii r= 90rrc light ray travelling from more dense to less dense medium refraction occurs refracted ray bends away from the normal. As the angle of incidence gets bigger, angle of refraction gets bigger & eventually becomes 90o. This angle of incidence is called the critical angle GlassGlassGlassAirAirAirAngle of incidence becomes bigger than the critical angle then..Total internal reflection occurs

* r= 90cGlassAirIt is possible to calculate the refractive index using the critical angleAs the angle of incidence gets bigger, the angle of refraction gets bigger & eventually becomes 90o. This angle of incidence is called the critical angleRefraction

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*Critical angle of glass in prism 41.9o (approx) Light from air to glass at 90o Light attempting to go from glass to air but angle of incidence greater than critical angle. No RefractionTotal Internal Reflection Light from glass to air at 90oNo Refraction

*Critical angle of glass in prism 41.9o (approx) Light from air to glass at 90oNo Refraction Light attempting to go from glass to air but angle of incidence greater than critical angle. Total Internal Reflection Light from glass to air at 90oNo Refraction

*Light rays from skyMirage ---- Total Internal Reflection of light from sky

*Real depthApparent depth n = Real depth Apparent depthGlass of waterRefraction

*Optic FibreGlass core of high refractive indexGlass cladding of low refractive index

*NormalNGlass of high refractive indexGlass of low refractive index