Enthusiastic Yr 13’s Studying Electromagnetic Induction
Electromagnetic induction is by no means a straight forward topic to get your head around whether you study Physics or not. It comes with a lot of terminology, definitions and understanding of magnetic fields and their interaction with motion.
Last period on Friday (after the students’ first week back after the Summer holiday), the students needed to get some blood flowing after recapping and learning the definitions for magnetic flux density, magnetic flux and magnetic flux linkage, which I have outlined here if you are interested:
The students took a long wire (approximately 15 m in length) made a loop where both ends were connected to a galvanometer, this is an instrument used for detecting very small electrical currents. Putting it simply, they held in their hands a long wire in one big loop connected to an ammeter and nothing else.
To the Hokey Cokey song, the moved in and out, shaking that wire all about! See what happened to the ammeter.
What did they learn?
What they learned was that they were linked with the magnetic field of Earth!
Earths magnetic field is tiny and about 50 μT, yet we can see its affects in a classroom by doing a little dance!
If their faces weren’t blurred you would be able to see how much fun they were having! I almost got them to do this on the playground, but felt that the sixth formers may never want to show up to my lesson again.
Explaining these observations
By linking the wire to the galvanometer and moving in and out of Earths magnetic field they were inducing an e.m.f. When they were stationary, the galvanometer was stationary showing no signs of an induced e.m.f. This should make sense to us as without their input of energy, they would not have been able to induce a form of electrical energy (conservation fo energy).
So the magnetic flux linkage induced an e.m.f. WHEN they moved through the field. Michael Faraday observed this in 1831 and wrote a law to explain things:
The e.m.f induced is proportional to the rate of change in magnetic flux linkage. As an equation he wrote this as:
That… was where we ended the lesson. I’m looking forward to reviewing it and getting them to learn Lenz’s law next!
The only thing that interferes with my learning is my education.