This preview shows pages 1–5. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Physics 344 Foundations of 21 st Century Physics: Relativistic and Quantum Systems Instructor: Dr. Mark Haugan Office: PHYS 282 [email protected] TA: Dan Hartzler Office: PHYS 7 [email protected] Grader: Fan Chen Office: PHYS 222 [email protected] Office Hours: If you have questions, just email us to make an appointment. We enjoy talking about physics! Help Session: Thursdays 2:00 – 4:00 in PHYS 154 Reading: Chapters 2 and 3 in Six Ideas that Shaped Physics, Unit Q Announcement: Homework 10 due Friday. Next week, homework 11 will overlap. Interference and the Wave Model of Light Last time, we predicted the intensity of light reaching a distant screen from two sources oscillating in phase by considering points on the screen one at a time and focusing on the difference in the length of the paths to the chosen point from each of the sources. Q2. What is the path difference, Δ l = d sin θ , if the chosen point C is located at the first place the intensity falls to zero as you move it away from the central maximum of the interference pattern? A) λ /4 B) λ /2 C) 3 λ /4 D) λ E) 2 λ Q1. What is the path difference, Δ l = d sin θ , if the chosen point C is located at the first place the intensity falls to zero as you move it away from the central maximum of the interference pattern? A) λ /4 B) λ /2 C) 3 λ /4 D) λ * * Interference and the Wave Model of Light d (N1)d θ In recitation, we used the same approach to conclude that the principal interference fringes produced by a diffraction grating ( N sources oscillating in phase) are much narrower than in the 2source case. L λ ∆ = / 2 λ With 2 sources, the first interference zero occurs when ∆ l = λ /2 = d sin θ . With N sources, it occurs when ∆ L = λ = (N – 1)dsin θ N , since this means that first and middle sources are out of phase and since all the remaining sources can be paired with a similarly out of phase partner. The principal (brightest) fringes occur when all of the sources are in phase, so, at the same angles as the 2source fringes. Since their location depends on λ the narrow fringes of a grating efficiently separate light by color, sending different λ s in different directions x z L d << L 1 k a 1 2 2 k a Interference Revisited Last time, we also realized that we were going to have to develop a more sophisticated photon model of light to explain the appearance of interference fringes in the low intensity version of the 2slit experiments we discussed. screen To do that we must have a model of the “beam” of light that reaches the screen in such experiments, not simply a prediction of where the fringes are. Since the screen is far from the sources, the electromagnetic field is a superposition of two essentially plane waves with the same frequency and nearly parallel wave vectors in the neighborhood of screen’s center, where we’ve located the origin of our coordinate system....
View
Full
Document
This note was uploaded on 12/09/2011 for the course PHYS 344 taught by Professor Garfinkel during the Fall '08 term at Purdue University.
 Fall '08
 Garfinkel
 Physics

Click to edit the document details