R EFRACTION OF L IGHT W HAT IS R EFRACTION Although light travels in straight lines, it bends when it passes from one medium to another Refraction: the bending of light rays as they pass between two different media W HY D OES R EFRACTION O CCUR ? Refraction occurs due to changes in the speed of light in different mediums Different media slow down light by different amounts The more that light slows down, the more the light is refracted R EFRACTION IN W ATER Demo: Disappearing Coin Light rays change direction at the surface of the water The image of the coin appears to be more shallow than the actual coin R EFRACTION IN W ATER F ERMAT S P RINCIPLE Light will follow the path that takes the least amount of time In a single medium, the pathway is always a straight line When travelling from one medium to another the fastest pathway is not a straight line Which path from A to B is faster? A NGLE OF R EFRACTION Refracted ray: ray of light that is bent when entering a second medium Angle of refraction: angle between the normal and refracted ray A NGLE OF R EFRACTION When travelling from a less dense medium to a more dense medium, light bends towards the normal When travelling from a more dense medium to a less dense medium, light bends away from the normal I NDEX OF R EFRACTION Speed of light in a vacuum: 3.0 x 10 8 m/s Speed of light is less than this in any type of matter Index of refraction is easier system for describing relative speeds The amount by which a transparent medium decreases the speed of light I NDEX OF R EFRACTION No units: they cancel! or Given: Speed of light in glass = 1.91 x 10 8 m/s Speed of light in vacuum = 3.00 x 10 8 m/s = 1.57 = 3.00 x 10 8 m/s 1.91 x 10 8 m/s The refractive index is 1.57 Given: Refractive index in water = 1.33 Speed of light in a vacuum = 3.00 x 10 8 m/s v = 2.26 x 10 8 m/s 1.33 = 3.00 x 10 8 m/s v The speed of light in water is 2.26 x 10 8 m/s D ISPERSION Dispersion: the refraction of white light into separate wavelengths (colours) The amount of refraction is different for each colour Different colours of light travel at different speeds so each refracts a different amount RRR (Red Refracts Rotten) BBB (Blue Bends Best) D ISPERSION O BSERVING & T RACING R EFRACTION A CTIVITY Materials: Laser level Plastic block White board Marker Procedure: 1. Shine the laser on one side of the block. Observe the incident and refracted rays at different angles of incidence 2. Draw 1 incident ray on one side of the block (IR1) 3. Shine the incident ray along IR1. Mark the ray that emerges from the other side as refracted ray 2 (RR2) 4. Connect IR1 with RR2 inside the block with straight lines O BSERVING & T RACING R EFRACTION A CTIVITY Analysis: Label what you think is refracted ray 1 (RR1) and incident ray 2 (IR2) Draw a normal on both surfaces of the block Measure i1, R1, i2, R2 What do you notice about i1, R2? How about i2, R1? H OMEWORK Page 456 # 1 8 S NELL S L AW There is a relationship between the angles of incidence and refraction of the indices of refraction of 2 media (n) Snells Law applies to refraction of light in any situation regardless of the media S NELL S L AW Q UESTIONS 1. Light passes from air (n = 1.00) into diamond (n = 2.42) with an angle of incidence of 60.0 degrees. What is the angle of refraction? 2. What is the index of refraction of a material if the angle of incidence in air is 50.0 degrees and the angle of refraction in the material is 40.0 degrees? 3. A diamond ring is dropped into water. The index of refraction for diamond is If light strikes the diamond at an angle of incidence of 60.0 degrees, what will be the angle of refraction in diamond?