I was introducing single slit diffraction the other day. I shone a laser through a variable width slit and showed that when I narrowed the slit the light spread more. I wanted students to take some measurements but it would not be easy for them to measure slit width so I directed them towards Walter Fendt’s single slit diffraction applet. They were able to quickly plot a graph of wavelength against angle of first minimum and also slit width against angle of first minimum. I thought it was a really good introduction to the topic because students asked lots of questions about the shape of the diffraction pattern, where to measure to etc. I found myself saying good question, we are going to explain that in the next lesson on quite a few occasions.
Triple A Learning IB Blogs
February 5, 2012
February 18, 2011
Doppler Effect – Anyone done any measurements?
Like most Physics teachers, I do several demos of the Doppler Effect in class but I never take any quantitative measurements. The following YouTube clip of a fire engine has terrible video but the effect is very noticeable.
February 10, 2011
Simple Harmonic Motion lesson 1
In a recent workshop several teachers asked me if it is possible to teach SHM without using calculus. I do. It is very tempting to do some differentiating but unless all your students have studied calculus this will confuse them. In my class studnets are doing different maths courses and only a few of them have studied differentiation when I teach SHM. Most studnets find SHM one of the more challenging topics. I think this is because they are introduced to several new equations and it is a completely new topic to them. (something they have not met in earlier grades)
Here is my approach to teaching SHM
Simple Harmonic motion Lesson 2
After introducing the pricipals and equations for SHM it is important to give students practice with the many new equations they have learned. I think students always like to solve some straightforward numerical problems to help get familiar with new concepts. There are several equations in SHM so it is important that they have time to get a feel for the equations. I like to tell them that the equation v = ωxocosωt can tell them how fast a pendulum is going at a certain time and then introduce v = +/-ω √(x02-x2) which can tell them how fast a pendulum is going at a certain position.
It is always nice to derive new equations but I dont do this for this equation. I use a qualitative approach. When x = 0 v will be maximum and when x = x0 which agrees with what they already know.
