class25lecnotes

class25lecnotes - -thIs is'Sn~ll-ia;hich tells us that...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
-- thIs is 'Sn~ll' ;-ia;:;hich tells us that light bends when it moves from one medium with a given index of refraction into a medium with a larger index of refraction. In this context, we briefly describe the procedure through which w~ analyze refraction. I ~ ~r I ~ ~ ~ "'" ~ " \'\J I"- ~, N ~ 1\. i'f'l 'S ~l ' "" \ .... 1. Represent the light beam with one ray. ~ ...... 2. Draw. the perpendicular to the interface at the point where the ray hits the , I interface. Label the angle ofineidenee'Ol (with respect to the perpendicular!). 3. Show how this incident ray is bent upon passing beyond the interface, labeling the 'I ~ angle of refraction O 2 (again with respect to the perpendicular). " 4. Repeat the procedure, if there is more, than one interface. ~. 5. Use Snell's Law to compute the index of refraction. .... ~ ): ;,;::
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
----- (/Jd . .r) Example 1. A laser beam is aimed at a lcm thick sheet of glass at an angle of 30 0 above the glass surface. A) What is the beam's direction of travel in the glass? B) What is its direction in the air on the other side of the glass? C) By what distance is the beam displaced with respect to its original direction? tt _ 2 Vz.- . (I, ~ riu &, ~ I?, f/11 &z j = ) .u.;.. ~ ~ 1?'.$iM. ~ /?, - I I flz. - n ~ __ "':::";'--"-_~ ___ _ t<r.l(}.M 11= I.S I = > '..1 AM 6t2°__ VI fi .) fin (7l. .: - - =_ c. () . .J9 I . .r z·!) 1 :.;> L &,. ~ s r: 1 j t} &3; e z 4 ~~ :: ~ ) I'1us WI4 /./dl'UI dul ~ ~ (a-til) 611-ac tiolJ-JJ.]~,:: < 1: ;I 0 1=111 C .: ~-4 /MAti /J ,48b: ;) 1M:: /)f) tl:JtJi Being able to write down Snell's Law, and solving problems based on it does not, however, mean that we understand refraction. Snell's Law tells us how light bends. It does not tell us why it bends. We can provide a somewhat deeper answer in terms of the Least-Time Principle: It bends in order to minimize the travel time between two given points on either side of the refracting surface. Light has to shorten its path through a medium with a larger index of refraction because through that medium it moves at a lower speed. We have long guessed that the index of refraction must have something to do with the ratio of the speeds of light through the two media: {n:; Clv]
Image of page 2
This connection was not clear at the time Snell worked out his law. Light is an electromagnetic wave, which has the special property of being able to propagate through nothing (vacuum). This is possible, so we learned, because the electric and magnetic fields that oscillate in an electromagnetic wave can regenerate each other. A changing electric field enforces a changing magnetic field through a process called induction, and vice versa. All electromagnetic waves travel at the speed of light. When an electromagnetic wave reaches a medium, e.g our atmosphere, windows, etc., these oscillating electric fields are forcing charged particles within the material to respond to the oscillation and accelerate back and forth with it. This periodic acceleration gives rise to a new source of changing electric fields. Consequently, instead of the initial "simple" situation of an electromagnetic wave originating from OJlt source, we now have a complicated collective vibration of all the charges in the material. These induced fields add up onto the initial source fields. This complicated situation is described by a set of
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern