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Interference of two Circular or Spherical Waves - a Lesson Plan

Eleni Kyriaki teaches Science and ICT in Belgium. In the article below, she shares with you a lesson plan entitled: “Interference of two Circular or Spherical Waves”. It is intended to be a useful source of information and inspiration for a target group of secondary level students (aged from 16 to17).

Lesson Title: Interference of two Circular or Spherical Waves

Curriculum Subject: Physics

Age of students: 16-17 (Secondary Level students)

Required background:
Oscillation – Oscillation Amplitude – Period - Frequency
Wave – Wavelength
Superposition Principle
Pulse Addition [3]

Related Historic Experiments
Young Interference Experiment

Objectives
Students will be able to:

• Apply the Superposition Principle in waves
• Work on the pattern derived from the experiment in order to find the constructive and destructive points of the elastic medium
• Work with the set of equations and find the same pattern (explore using simulations)
• Experiment with water, sound and light waves in real or web experiments.

Didactic Approach
The phenomenon of the interference of two circular or spherical waves is quite complex. You need to demonstrate static pictures, simulations and real or web experiments to give an accurate picture of the phenomenon to your students.
The students must realize that to explain the complicated patterns, you have to work point by point on the elastic medium. To draw the correct conclusions, precision, imagination and a good mathematical background are required.

Lesson Plan

1st Lesson

• Step 1 (10 min)
  
  - Try to start your lesson by a real experiment.
  - If you can’t, use a static picture or a first demonstration of the simulation program (virtual experiment).
  
  
• Step 2 (20 min)
  
  - Draw on the blackboard the product of the interference of two circular or spherical waves of the same wavelength derived by two sources oscillating with the same amplitude and the same phase.
  - You may choose an easy drawing by taking the distance of the sources four times bigger than the wavelength.
  - Examining the result in 4-5 points on the “elastic medium” is enough; the students must notice that the difference of the distances from the sources is related to the constructive and destructive result at each point.
  
  
• Step 3 (10 min)
  
  -Give the opportunity to your pupils to work in small teams with the simulation program.
  - Worksheets encouraging them to try out different values of sources distance and wavelength will help them observe and explore.
  
  
• Step 4 (5 min)
  
  - Conclusions
  

2nd Lesson

Figure 1: The interference of waves demonstrated by Walter Fendt's applet

• Step 1 (5 min)
  
  - Repeat the demonstration of the simulation
  - Discuss the conclusions from the previous lesson
  
  
• Step 2 (15 min)
  
  - Present the theory explaining the phenomenon and the set of equations.
  
  
• Step 3 (5 min)
  
  - Demonstrate the simulation program: point out that the simulation is based on the equations.
  
  
• Step 4 (15 min)
  
  - Exercises
  
  
• Step 5 (5 min)
  
  -Conclusions
  

Resources
[1]  The Xplora-Knoppix DVD which is distributed from the Xplora repository
[2]  Walter Fendts JAVA applets
[3]  Pulse Addition 

Contact
Eleni Kyriaki