## Lesson 3: Diffraction and Interference of Water Waves

## Overview:

In this lesson, we will explore what happens when water waves, and sound waves interfere. Then we can generalize this behaviour and create an operational definition of a wave. That is, if a phenomena shows the interference pattern then it is a wave!

## Curriculum Expectations:

**Overall Expectations:**

**E2.**Investigate, in qualitative and quantitative terms, the properties of waves and light, and solve related problems.

**E3.**Demonstrate an understanding of the properties of waves and light in relation to diffraction, refraction, interference, and polarization.

**Specific Expectations:**

**E2.1**Use appropriate terminology related to the wave nature of light, including, but not limited to: diffraction, dispersion, wave interference, nodal line, phase, oscillate, polarization, and electromagnetic radiation.

**E2.2**Conduct inquiries involving the diffraction and interference of waves, using ripple tanks or computer simulations.

**E2.4**Analyze diffraction and interference of water waves and light waves (e.g., with reference to two-point source interference in a ripple tank, thin-film interference, multiple-slit interference), and solve related problems.

**E3.1**Describe and explain the diffraction and interference of water waves in two dimensions.

## Success Criteria:

- Describe diffraction.
- What happens if you change the wavelength, but keep the slit width fixed?
- What happens if you change the slit width, but keep the wavelength fixed?
- If waves are to undergo more noticeable diffraction, then what has to be true about the relation between the wavelength and the slit width?
- What is wave interference? And what conditions are necessary for the interference pattern from a two-point source to be stable?
- Describe using diagrams the conditions required for constructive and destructive interference of waves.
- Describe using a diagram in a two source interference where nodal and anti-nodal lines occur.
- Define path length and path length difference.
- In general if a point P is on a nodal line, then is the path length difference a half or full wavelength multiples?
- How can you determine the angle that a nodal line makes with the right bisector?
- How can you measure the distance from the right bisector of the screen to the nth nodal line?

## Time Allocation: 4 hours

## Learning A

ctivities:**Read**pages 459 - 468 from Nelson 9.3

SoundThis simulation lets you see sound waves. Adjust the frequency or volume and you can see and hear how the wave changes. Move the listener around and hear what she hears. |

In the playlist below, video:

- Will show you how to calculate I=? when there is sound (or wave) interference.
- Will show you how to calculate x=? where there is constructive and destructive interference.

**Practice**questions 1 and 2 on page 461.

**Practice**questions 1, 2, and 3 on page 468.

## Task:

**Solve**question 4 from Nelson 9.3 Review on page 469.

*Optional Extension:*- Solve questions 3 on page 469.

## Reflect:

How would you explain the concepts of total internal reflection, refraction, and diffraction to a fellow student who has not taken physics?