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Snell’s Law

Snell’s Law. Index of Refraction (n). POLAR BEAR REFRACTION at the SENECA PARK ZOO. REFRACTION. N. Why does light bend?. fish tank. Refraction. The travel of light from one medium to another: Change in wave speed change in wavelength Change in direction No change in frequency.

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Snell’s Law

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  1. Snell’s Law Index of Refraction (n)

  2. POLAR BEAR REFRACTION at the SENECA PARK ZOO

  3. REFRACTION N Why does light bend? fish tank

  4. Refraction • The travel of light from one medium to another: • Change in wave speed • change in wavelength • Change in direction • No change in frequency

  5. li lr REFRACTION N li >lr incident ray fi = fr Qi fast slow Ray bends toward Normal refracted ray Qr

  6. li lr REFRACTION N li <lr incident ray fi = fr Qi slow fast Qr Ray bends away from Normal refracted ray

  7. N Fast to Slow Slow to Fast N Qi Qi fast slow slow fast Qr refracted ray bends toward N refracted ray bends away from N Qr

  8. n = c v n a 1 V Index of Refraction (n) (speed of light in vacuum) (speed of light in a given medium) c = 3.0 x 108 m/s The bigger the n value, the slower the light travels.

  9. MATERIALnv AIR 1.0003 ~ c WATER 1.3 .77c GLASS 1.5 .67c DIAMOND 2.4 .42c n = c v Index of Refraction (n)

  10. l1 l2 SNELL’S LAW N sin Q1 = l1/hyp V1<V2 sin Q2 = l2/hyp Q1 V1 medium 1 (slow) Q1 Q1 hyp medium 2 (fast) Q2 Q2 Q2 V = f l V2 f1= f2 V al

  11. V1 sin Q1l1 = sin Q2l2 V2 n a 1 V Snell’s Law n2 = = n1 V al n1 sin Q1 = n2sin Q2

  12. N N N Critical Angle (Qc) Qi Qi Qc glass air Qr = 90 Qr Qr If the incident angle is equal to the critical angle, the refracted angle = 90

  13. N Total Internal Reflection reflected ray Qi>Qc glass air If the incident angle is greater than the critical angle, the boundary behaves like a perfect mirror.

  14. Total Internal Reflection Qi>Qc FIBER OPTIC CABLE: LIGHT PIPE

  15. sin Qc = 1 n1 Total Internal Reflection n1 sin Q1 = n2sin Q2 (slow medium) (fast medium) If material #2 is air, n2 =1 If:Q1 = QcThen:Q2 = 90 n1 sin Qc = 1sin 90 = 1

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