Snell’s Law A way to figure out exactly how much light will bend!! Students in grade 10 math – try examples
To be included on Formal Lab Introduction Purpose (one for both) Hypothesis - Not required Materials (one for both) Procedures (A & B) Observations (A & B) Sample Calculations Error Analysis - precision of instrumentation Discussion Questions (1-7 & 1-8) Diagrams Conclusion
Diagrams
Review: Light travelling from fast to slow bends TOWARDS THE NORMAL Light travelling from slow to fast bends AWAY from the NORMAL HIGH “n” means material is SLOW LOW “n” means material is FAST
Amount of Refraction The amount of refraction will depend on – The difference in the speeds of the two materials The bigger the difference, the more refraction occurs – How big the angle of incidence is the bigger it is, the more refraction will occur
Snell’s Law OR
What is “sin”? Stands for sine and it is a mathematical term. It represents the ratio of the length of the side opposite of a certain angle to the length of the hypotenuse in a right angle ( ) triangle adjacent
e.g sin = This means that the side opposite to the angle is half the length of the hypotenuse. This could mean that possible triangles are Side A: 0.5 cm, Side B: 1 cm Side A: 1 cm, Side B: 2 cm Side A : 20 cm, Side B: 40 cm A B You will learn more about it in grade 10 math, so for now we will mostly learn how to use it for Snell’s Law only…
In order to properly use the sine ratio: First – make sure your calculator is set on degrees!!! To get sin 30 o, just press sin and then 30 on your calculator! (for some calculators you have to press 30 then sin) Check the others in the table…
A little harder to remember… e.g. if you are told that and asked to find then you have to use the “second function” button and sin -1 Notation important!
medium # 1: Slow medium #2: Fast normal incident ray refracted ray ii rr
Rearranged versions that are maybe easier to memorize: or So long as the order is met, subscripts are completely arbitrary and you can choose any letters that suit the situation in order to make Snell’s Law easier to work with during the question
1. Calculate the index of refraction of cubic zirconium (fake diamond) if the angle of incidence in water is 50.0 o and the angle of refraction in the cubic zirconium crystal is 27.0 o. (Note: the index of refraction of water is 1.33) 50 o 27 o Water n w=1.33 Cubic zirconium n z= Index of refraction of zirconium is about Make sense? n z is bigger than n w this means that cubic zironium is slower than water Refracted ray should bend towards the normal It does!!! Makes sense!!!
2. When light passes from crown glass (n=1.52) into ice (n=1.31) at an angle of incidence of 30 0, what is the angle of refraction? 30 o The angle of refraction would be about 35 0 (bends away - makes sense)! n g is bigger than n i light is moving from slow to fast Should bend away from the normal Crown glass n g =1.52 Ice n i =1.31
Common errors: This is not the same as the x -1 button we used for the mirror equation. If you get an error message, you were probably trying to do sin -1 to a number bigger than 1 which is impossible…(it is impossible because the hypotenuse has to be the longest side and You can’t divide by sin…has to have an angle with it!