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# P5g Refraction Of Waves Investigation Notes

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### P5g Refraction Of Waves Investigation Notes

1. 1. P5g - Refraction of waves Refraction is…
2. 2. Refraction
3. 3. Refraction <ul><li>When waves slow down, the wavelength gets shorter </li></ul><ul><li>When waves speed up, the wavelength gets longer </li></ul><ul><li>This causes the wave to change direction unless it is traveling along the normal. </li></ul>
4. 4. Refraction investigation <ul><li>Intro </li></ul><ul><li>You are going to calculate the refractive indices and critical angles for glass and perspex blocks </li></ul>
5. 5. Refraction investigation <ul><li>Method </li></ul><ul><li>Watch the brief intro </li></ul><ul><li>Draw up 2 results tables, one for glass and one for perspex </li></ul><ul><li>Collect your apparatus </li></ul><ul><li>Repeat each experiment at least 5 times using the same angle i. </li></ul>
6. 6. Refractive index (n) <ul><li>n = speed of light in a vacuum </li></ul><ul><li>speed of light in the medium </li></ul><ul><li>n = 300 000 000 m/s </li></ul><ul><li>speed of light in the medium </li></ul>
7. 7. Refractive index (n) n = speed of light in a vacuum speed of light in the medium Q ~ What is n for a) air b) water 225 000 000 Water 299 900 000 Air 300 000 000 Vacuum Speed of light (m/s) Medium
8. 8. Snell’s law i r n = sin i sin r medium i medium r “ Angle of refraction depends on the refractive index”
9. 9. Snell’s law n = sin i sin r Q ~ If the medium is water (n = 1.33) and angle i is 30  , what is angle r ? r = 22  n = sin i sin r 1.33 = sin 30 sin r sin r = sin 30 1.33 sin r = 0.5 = 0.38 1.33
10. 10. Snell’s law n = sin i sin r Q ~ In another medium, if i is 30  and r is 12  , what is n? Q ~ If the medium is water (n = 1.33) and angle i is 40  , what is angle r ?
11. 11. Refraction investigation <ul><li>Analysis: </li></ul><ul><li>Calculate n for air/glass and air/perspex interfaces using your experimental results </li></ul><ul><li>Pick one result from each material and use angles i and r </li></ul><ul><li>Use Snell’s law (n = sin i / sin r) to work out your values for n. </li></ul>
12. 12. Refractive index between 2 media i r medium i medium r n = n r n i
13. 13. Refractive index between 2 media i r water (n = 1.33) air (n = 1.0) = 0.75 n = n r n i n = n air = 1.0 n water 1.33
14. 14. Refractive index between 2 media i r water (n = 1.33) glass (n = 1.5) = 1.12 n = n r n i n = n glass = 1.5 n water 1.33
15. 15. Refraction investigation <ul><li>Analysis </li></ul><ul><li>You can now calculate the refractive indices (n) for glass and perspex </li></ul><ul><li>Use your results n air/glass and n air/perspex </li></ul><ul><li>Assume that n air is 1.0 </li></ul>
16. 16. Refraction investigation i r air (n = 1.0) glass (n = ?) n = n r n i n glass = ? n = n glass = n glass n air 1.0
17. 17. Refraction investigation i r air (n = 1.0) perspex (n = ?) n = n r n i n perspex = ? n = n perspex = n perpex n air 1.0
18. 18. Refractive index and critical angle “ Total internal reflection”
19. 19. Refractive index and critical angle n = n r n i = sin i sin r = sin c sin 90 n r n i = sin c n r n i sin 90 = 1
20. 20. Refractive index and critical angle = sin c n r n i <ul><li>Refraction investigation </li></ul><ul><li>Now, using your results you can calculate: </li></ul><ul><li>The critical angle for glass </li></ul><ul><li>2) The critical angle for perspex </li></ul><ul><li>We will check your answers with a practical next lesson </li></ul>