 Physics Core/AP 1 and 2

#### Course Materials are always under revision! Weblecture content may change anytime prior to two weeks before scheduled chat session for content. Homework

# Physics 24: 1-5 Light Transmission Through Media

## Homework

### Reading Preparation

Text Reading: Giancoli, Physics - Principles with Applications, Chapter 24: Sections 1 to 5

##### Study Points
• Section 1: Huygen's Principle: Every point on a wave front can be considered as the source of tiny wavelengths that spread out in the forward direction at the speed of the wave. The new wave front is the tangent to the wavelets. This explains the phenomenon of diffraction where the edges of a barrier act as the "source" of new waves.
• Section 2: When light travels from one medium to another, frequency remains constant, but wavelength changes and velocity changes: v = λν.
• Section 3: Following the laws of superposition, two waves will add their amplitudes at a given point. If the result is a net increase (both waves up or both waves down), the interference is constructive If the result is a net decrease in amplitude, the interferences is destructive. The double-slit experiment demonstrates constructive and destructive interference in the pattern of maxima and minima intensities that forms on a reflective surface opposite the slits.
• Section 4: In light, the frequency or wavelength is related to the color of light in the visible range. The intensity of light is the energy carried per unit area per unit time: it is power per unit area (as we saw with sound). Refraction of light in a medium depends on wavelength. Blue bends better; red refracts reluctantly.
• Section 5: Diffraction patterns also form from single slits.

### Key Equations

• Snell's Law from Huygen's Principle:
• Wavelength of light in new medium with index of refraction n:
• Constructive interference diffraction (bright)

d = distance from central axis opposite slit
θ = angle from slit along axis to band
l (distance between slit and screen) >> d

• Destructive interference diffraction (dark)
• First minimum:

D = slit width

### Web Lecture

Read the following weblecture before chat: The Wave Nature of Light

### Study Activity

Use the interactive activity to explore the implications of Snell's law.

• Click on the introduction panel.
• Turn on the laser. What happens to the beam of light as it hits the interface between air and water?
• How is the angle of reflection related to the angle of incidence?
• How is the angle of refraction related to the angle of incidence?
• What happens if you reverse the media, so light starts in water and then enters air?
• Explore at least two other pairs of media. Use Snell's law and the information about the index of refraction to predict the angles of reflection and refraction, then use the protractor to measure the experimental values.
• Use the intensity meter to determine how much light is reflected and how much is refracted at each interface. How are these values related to the density of each medium?
• Repeat your observations using the wave visualization.
• Use the "More tools" option to explore light reflection and diffraction by measuring speed and time, and vary the wavelength.

Physics simulation Java Applets are the product of the PHET Interactive Simulations project at the University of Colorado, Boulder.

### Chat Preparation Activities

• Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
• Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

### Chapter Quiz

• The chapter quiz is not yet due.

### Lab Work

If you want lab credit for this course, you must complete at least 12 labs (honors course) or 18 labs (AP students). One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!