Unit 4 lab practical – Exploring wave interference

Part 1 - Prior Knowledge Question: (Do this BEFORE starting the practical.)

On a trip to the lake, a boy starts to skim stones across the water. He measures how many bounces he is capable of by the pattern left in the water by the stone.

1. The ripples created by the stones are an example of waves – in the space below describe what a wave is in your own words.

2. Using your understanding from the definition in part 1, explain how a skimming stone creates waves?

Part 2 – Exploring waves:

Waves come in many different forms: water waves, light waves, and sound waves are just some examples. The Wave interference sim allows you to explore the key features and characteristics of waves.

You can explore the simulation by going to the following link:

https://phet.colorado.edu/sims/html/wave-interference/latest/wave-interference_en.html

1.   To begin:

A.  Select the ‘Waves’ simulator.

B.  Make sure that water waves is the mode selected (this is the default setting when you open it).

C.  Make sure the ‘Graph’ setting is switched on.

2.   Play around with the sliders for frequency and amplitude - see how each of these affect the ripples being created.

3. Exploration and experimentation 1: Use your own words and captured pictures from the simulation to show how you can produce the following:

a.  Waves of the longest wavelengths possible.

b.  Waves of the Shortest wave possible.

c.   Waves of the tallest wave possible.

d.   Describe and explain your experiments to make waves of different wavelengths and heights (including what views and tools you used and why). Support your explanation with pictures form. the sim.

4. Exploration and experimentation 2: Use your own words and captured pictures from the simulation to show how you can measure the following:

a.   Period of the longest, shortest, and tallest wave possible.

b.   Speed of the longest, shortest, and tallest wave possible (recall our wave equation used to calculate velocity of a wave).

c.   Summarise your understanding of wave characteristics and behaviours by comparing the longest, shortest, and tallest waves. (Use the vocabulary words: wavelength, wave speed, amplitude, frequency).

Part 3 – Waves and interference patterns:

Part 3A: Sound waves:

0. Set up:

a. Change the simulator to the ‘ interference’ sim.

b. Set the type of wave as ‘sound’ waves. This is done by selecting the speaker on the right hand side.

c. Make sure the ‘graph’ setting is switched off.

d. Make sure only the ‘wave’ view is turned on.

1. Predict: Look at the following patterns: they were created by only adjusting one setting – which setting do you think it was?

2. Exploration and experimentation 1: Test your prediction by trying to replicate the patterns seen above – was your prediction from section 1 correct? If yes - explain how you created the  patterns, if no – explain which settings you used to create the pattern and how.

3. Explore and experimentation 2: Do you think there is more than one way of replicating the patterns from above? Experiment with other settings and see if you can reproduce the patterns once again, explain your process and what did and didn’t work.

Part 3b: Light waves

1. Set up:

a.   Change your wave type to light waves. This is done by selecting the laser pointer on the right-hand side.

b.   Change your light frequency to whatever colour you prefer.

c.   Make sure that ‘graph’ and ‘screen’ are both unselected.

2. Predict: Look at the diagram below, highlight where you think the points of constructive and destructive interference are found.

3. Exploration and experimentation 2: Create a similar wave pattern using your simulator, use the light detector tool (in the top right box) to find points of constructive and destructive interference.

4. Explain: How did you recreate the pattern, and how did you use the light detector tool – use the space below to describe your method and results.

Part 4 – Diffraction and slit interference:

0. Set up:

a. Change the simulator to the ‘Slits’ sim.

b. Change your wave type to light waves. This is done by selecting the laser pointer on the right-hand side.

c. Select ‘no barrier’ from the menu.

1. Describe: How are the waves we are using here, different to the waves generated in our previous simulation?

2. Predict: What do you think will happen to the wave when we introduce a barrier?

3. Describe: What is happening to the waves when we introduce a singular slit?

A: Explain the phenomena in terms of the bending of light waves. (Hint: Recall Huygens’ theory of wavelets).

B: What would we expect to see if we introduce a screen to the far end of the experiment?

4. Describe and explain: If we introduce a second slit, what happens to the pattern that we see on the screen? What is creating the pattern?

5. Calculate: Using the red light and the distance measuring tool – see if you can calculate the wavelength of the light. (Recall our relationship is as follows: (PS1 – PS2) = mλ)