1. Phy2005 Applied Physics II Spring 2016 Announcements: Makeup solns, grades, HITT grades posted Make-up exam average 68% Note changes in last 2 weeks of syllabus Final exam: 50% Chs. 19-25 50% Chs 26-29

2. Science news page PBS Link SpaceX finally lands successfully on barge at sea

3. For those of you bitterly disappointed that there is no superconductivity on the official syllabus “Superconductivity: How Two Electrons can Attract Each Other and What it Might Mean to You Someday” Webcast

4. Diffraction Grating d   r = dsin  = m  Constructive provides much clearer and sharper interference pattern and a practical device for resolving spectra. Last time

5. xn Q1: A thin film of polymer used in an antireflective coating has an index of refraction of 1.5. If light of frequency 5.5 x 10 14 Hz is incident on the film, but is found to be entirely transmitted and not reflected, what is a possible thickness x of the film (in m)? (1)9.1 x 10 -8 (2) 1.8 x 10 -7 (3) 1.3 x 10 -7 (4) 0 (5) 3.6 x 10 -7 =c/f=(3.0 x 10 8 m/s)/(5.5 x 10 14 Hz)=5.45 x 10 -7 m in film f  =(c/n)/f= 5.45 x 10 -7 m/1.5 = 3.63 x 10 -7 m for destructive interference, 2x=  f /2, … so x=  f /4 = 3.63 x 10 -7 m/4 = 9.1 x 10 -8 m path diff = 2x

6. ACADEMIC HONESTY Each student is expected to hold himself/herself to a high standard of academic honesty. Under the UF academic honesty policy. Violations of this policy will be dealt with severely. There will be no warnings or exceptions.UF academic honesty policy

7. xn Q1: A thin film of polymer is 1.0 x 10 -7 m thick, and is to be used in an antireflective coating. The film has an index of refraction of 1.5. Which of the following wavelengths (in vacuum) will not be reflected (in m)? (1)9.1 x 10 -8 (2) 1.8 x 10 -5 (3) 1.3 x 10 -7 (4) 6.0 x 10 -7 (5) 3.6 x 10 -7

8. Diffraction the ability of waves to bend around obstacles In 19 th century, light is understood as a wave by work of Young and Fresnel and scientists searched for other wave phenomena in light. One of them is diffraction. Longer wavelength  more severe diffraction.

9. History: Fresnel’s theory of diffraction was criticized on the grounds that it implied that if you took a disk and blocked a beam of light with it, the diffraction around the edges would lead to an intensity maximum in the middle. “Ha! Ridiculous.” -- Poisson Arago: it works!!!!!

10. Single Slit Diffraction Pattern w cc sin  c = /w 1. When the wavelength of the light (wave) gets smaller compared to the slit size, the bright spot gets sharper (more particle-like). 2. When ≈ w,  c  90  (more wave-like).

11. Modern Physics 20 th century Special Theory of Relativity (Einstein 1905) General Theory of Relativity (Einstein 1916) Quantum Theory (1905-1925)

12. Newtonian Mechanics 1.In the absence of forces, a body moves with uniform speed in a straight line. (Law of inertia) 2. In the presence of force, the body changes its state of motion in such a way that

13. Newton’s laws of mechanics holds true in any inertial frames. Inertial frame: any coordinate system moving with a uniform speed relative to another inertial frame. This room is (almost) an inertial frame. Q: Why not quite? A: Because the Earth is rotating – our velocity is not uniform! Relative motion: According to Newton, a ray of light would go faster if shone from a moving train

14. z x y p = (x,y,z) z’ x’ y’ vt p = (x’,y’,z’) x’ = x – vt y’ = y z’ = z v x ’ = v x – v v y ’ = v y v z ’ = v z Newton Time t is the same in both frames t=t’

15. L In 19 th century, physicists believed in “ether” and that light travels with the speed of light, c relative to this light medium. Now, let’s consider the effect that we are making this measurement on the surface of the Earth which is moving through the ether with a speed v, close to 18 miles/s

16. Ether: a 19 th century misconception Acc. to 19 th century physicists, the Earth moves through the ether, the medium that supports light waves So from our perspective, the ether is like a wind blowing past us. Earth’s frame

17. Analogy: swimming in a current. Time to swim 400 feet || or  to current is different

18. L Light parallel to v L (with ether wind)

19. L 1 round trip time = 2L/c Light perpendicular to v Without ether wind With ether wind

20. Michelson-Morley’s experiment showed with a high precision t total = 2L/c for both directions  there is no such thing as the ether!!! Michelson-Morley (1887,…) experiment 1887 Case School

21. Accurate measurements of speed of light give the value c = 2.998 x 10 8 m/s no matter how the light source or/and the measurer are moving!! Serious conflict with then current understanding based on Newtonian world. Albert Einstein (1879 – 1955) In 1905, He provided a new view on space-time,and proposed a new theory of mechanics which is consistent with Newtonian mechanics in the limit of low speed. 1921 Nobel Prize in Physics “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect"