DAY 78

Goal:

SWBAT

1. describe patterns of constructive and destructive interference

2. properly create a setup to measure the width of human hair

WARM-UP

1. How wide is one piece of your hair? cm? mm? 0.1mm? more? less?

2. Another way of asking this question - how many hairs stacked side-by-side would be equivalent to the width of this line? ---> |

3. What is constructive interference?

4. What is destructive interference?

5. Copy the image from the board - how many wave patterns would be created by the object blocking the light source?

6. Does a laser light beam expand as it travels, or does it stay the same diameter?

CLASSWORK

078A: Review Refraction from Day 77 (VIDEO)

078B: "How wide is your hair?" Lab

LINK Read (skip #11). Also note that to save time, steps 1-4 will be different, as we will be mounting the hair directly to the front of the laser.

• Copy the data table from pg 7 into your notebook
• Materials: Ruler, strand of hair, tape, piece of paper, laser
• Discuss safety:

1. List three safety concerns:
2. To collect data, you'll need the laser on for an extended period of time. Should you tape the power button on? Why/Why not?
3. Lasers are fragile. Describe how you can handle them to keep them functioning.

• Practice time:
  • For successful data collection, you'll need to...
    • ...mount the hair to the front of the laser. Today we will practice that.
    • ...move your table or chair so that the distance between the hair and the target (paper on the wall) is less than or equal to one meter. Today we will practice that as well.
    • If you can get both of the above correct, I'll initial your data chart, and you'll be ready to begin the data collection portion of the lab tomorrow at the beginning of class.
• Data Analysis.
  • You'll be measuring the initial (close) and final (far) sides of each fringe. Why not just measure the middle of the fringe?
    • How do we find the average distance of each fringe from the central point?

Tomorrow we will collect data, and analyze the data you collect

HOMEWORK

Review the lab, as we will do it tomorrow.

Make up any late homework from the past week.

This Friday we will have an exam on Waves. You should update your Table of Friends (equation sheet), and begin reviewing.