Lecture%2035%202220%20Spring%202009

# Lecture%2035%202220%20Spring%202009 - Reminders and...

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1 Reminders and Announcements • HW 20 is due tomorrow; HW 21 is due Friday • Exam 3 is in one week Exam 3 is in one week • Help Room Hours (Physics 117): – M 4-8 pm, T 3-6:30, W 3-6:30, R 4:30-8, F 2-6 Snell’s Law of Refraction n 1 sin θ 1 = n 2 sin θ 2 θ 1 is the angle of incidence θ 2 is the angle of refraction 2 • The experimental discovery of this relationship is usually credited to Willebrord Snell and is therefore known as Snell’s law of refraction Example Example Huygens’s Principle • All points on a wave front are point sources for spherical secondary waves, called wavelets, which propagate with the characteristic speed of waves in that medium • The new position of the wave front is the surface tangent to the wavelets Huygens’s Construction – Examples Plane wave Spherical wave

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2 Huygens’s Principle and the Law of Reflection AD = BC = c Δ t Huygens’s Principle and the Law of Reflection, cont. • Triangle ABC is congruent to triangle ADC cos γ = BC / AC • cos = / • cos ’ = AD / AC • Therefore, cos = cos ’ and = • This gives θ 1 = θ 1 • This is the law of reflection Huygens’s Principle and the Law of Refraction • Ray 1 strikes the surface and at a time interval Δ t later, ray 2 strikes the surface • During this time interval, the wave at A
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Lecture%2035%202220%20Spring%202009 - Reminders and...

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