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Rogue Physicist.  Free resources for physics education © 2006-2016 Dorian Pascoe.  Email: dorian@top-school.co.uk

Most resources are available under a Creative Commons Licence.  Visit our mirror at www.physicsweb.altervista.org

 

 

 

...wave behaviour 2...

 

 

 

Objectives:

 

  
 

 

Waves!

  

 

• Know that waves can be diffracted, by passing through gaps or around obstacles.

 

 

• Be able to explain how the size of the gap will affect the amount of diffraction.

 

 

• Be able to draw accurate diagrams to show the diffraction of waves passing through a gap.

 

 

  

 

 

 

 

 

 

 

Task 1 - Starter

 

  
 

 

I know the answer!

 

 

  

 

Find someone who knows:

 

 

1) The law of reflection.

 

 

2) The three terms used to describe an image formed in a mirror, and what each term means.

 

 

3) What refraction is, and what conditions will cause refraction.

 

 

Your teacher will tell you which questions to discuss.

  

 

 

 

 

 

 

Task 2a - Diffraction

 

  
 

 

Lots of waves!

 

 

 

  

 

Waves tend to travel in straight lines - but this is not always the case...!  Look at this picture of waves passing into a harbour:

 

 

The wave fronts have become curved as a result of passing through the narrow gap between the harbour walls.  This effect is known as Diffraction.

 

 

  

 

 

 

 

 

 

 

 

Task 2b - Diffraction simulation

 

  
 

 

 

You will need the Yenka plug-in to run this software.

Download it here.

 

 

  

 

Look at this simulation of water waves passing through gaps of varying sizes, and around obstacles.

 

 

Click the image above to load the simulation.

 

 

What effect does the size of the gap have on the amount of diffraction?

 

 

You will find that:

 

• the size of the gap needs to be close to the wavelength.

 

• the smaller the gap the greater the diffraction effect.

 

 

 

Note: all Yenka software is free for home use; download the plug-in from the Yenka web site.  Schools and educational establishments will require a licence.

 

  

 

 

 

 

 

 

 

Task 4a - Diffraction diagrams

 

  
 

 

 

 

  

 

Draw 3 diagrams to show diffraction for each of the following scenarios:

 

 

• Diffraction through a gap larger than the wavelength.

 

 

• Diffraction through a gap equal to the wavelength.

 

 

• Diffraction around an obstacle.

 

 

Your diagrams should look something like this.

 

  

 

 

 

 

 

Task 4b - Describing diffraction

 

  
 

 

 

 

  

 

Complete the text below, by filling in the missing words:

 

 

 

Diffraction occurs whenever waves pass through a ______ or around an ___________.  This causes the wavefronts to become curved.

 

 

 

Significant diffraction only occurs when the ______________ of the wave is approximately _________ to the size of the gap.  As the size of the gap ____________ the diffraction effect becomes greater. 

 

 

 

This task will be available as a word document - at some point!

 

  

 

 

 

 

 

 

 

Homework

 

  
 

 

Let's catch some waves!

 

  

 

No homework task for this lesson.

 

 

Homework task coming soon!