Experiences

Interferention of the mechanical waves

Mária Dojčanová

Slovakia

High Secondary School

Physics

Teaching in class

Direct

The aim of the lesson is to express the conditions giving rise to the interference of mechanical waves describe this phenomenon and give conditions for the generation of the interference maximum and minimum.
The concept of mechanical wave interference phenomenon is new for the students. It is easier for the students to understand the phenomenon through a practical demonstration. In the lesson I use a short video from digital physics textbook by PaedDr. Joseph Beňuška. It is a throw of two stones on the water surface. This experiment we can do directly in the classroom, but in the video students have also the marked directions of the interference maximum - amplifying of the wave interference and interference minimum – the wave attenuation. To draw attention of the students I supplement the display of mechanical waves on the water with 2 films on which the waves with the same frequency are sketched. Students are usually fascinated by what happens when the foils are being consecutively shifted. I overlap them with the changing number of maxima and minima. Using the educational presentations and discussions from the digital physics textbook helps the students to understand the principle of superposition of waves when folding. From the animation pupils clearly understand the concept of "path difference waves" and the resulting emergence of waves of two. The latest topic is also available on video in the digital textbook. Through animations and videos pupils vividly perceive folding waves with the same phase and anti phase. During the mutual discussion they find out the resulting conditions for the interference maximum and minimum of the interference.
I can not even imagine how long it would take me to draw and write everything what I use from the digital textbooks. This way I can help pupils to understand the problem more quickly. In addition to briefing and demonstrations pupils alone, sometimes with a slight guidance write notes into their notebooks. In many cases I do not use all the available educational presentations for the topic but I only choose the ones that I need to explain physical knowledge. The reason for this is that sometimes I can not go into such depth as a digital textbook provides.
To reinforce new knowledge students answer questions that are in the form of a test at the end of any given topic in the textbook. Specifically for this topic they have an animation in which they should determine the interference maxima and minima.

The students really like the way of teaching using digital textbooks. I often grab attention even of those students who are not very interested in physics.