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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 Index of Refraction (n)
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
li lr REFRACTION N li >lr incident ray fi = fr Qi fast slow Ray bends toward Normal refracted ray Qr
li lr REFRACTION N li <lr incident ray fi = fr Qi slow fast Qr Ray bends away from Normal refracted ray
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
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.
MATERIALnv AIR 1.0003 ~ c WATER 1.3 .77c GLASS 1.5 .67c DIAMOND 2.4 .42c n = c v Index of Refraction (n)
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
V1 sin Q1l1 = sin Q2l2 V2 n a 1 V Snell’s Law n2 = = n1 V al n1 sin Q1 = n2sin Q2
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
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.
Total Internal Reflection Qi>Qc FIBER OPTIC CABLE: LIGHT PIPE
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