Sunday, 2 June 2013

Alternative Conceptions

One of the basic facts of science and mathematical education is that you have to deal with Alternative Conceptions in your students.
Basically humans are very good at finding patterns in the world, but we're very reluctant to give up on discovered patterns, even with plenty of evidence that they don't work. We also have a weird tendency to only seek evidence that confirms our theory, and discount or dismiss evidence that rules our theory out.
The following link lists a series of common Alternative Conceptions.

Van Der Graaf Machine - Preparation and Safety

Van Der Graaf machines are awesome - impressive as all hell, and allow you to investigate and demonstrate a large varieties of electrical physics concepts.

Typically I'm very much against the inductive-learning-good, deductive-learning-bad philosophy that has seemed to invade modern scientific theory. It takes too much time if done every lesson, it does little to correct pervasive alternative conceptions and it ignores half of how science works.

But a mixture of inductive and deductive learning works for Van Der Graaf machines. At the bottom of this post are some investigations that can be done. With good timing and a dollop (5 minutes) of deductive-style learning, you can complete most of them in a single one hour lesson.

Van Der Graaf - Miniature Lightning Bolts.

This earlier post outlines what you need to consider before doing any Van Der Graaf experiments.

This current post is the second in a series that describes some demonstrations that can be done with Van Der Graaf machines, including theoretical explanations.

The first demonstration is the simplest, throwing miniature lightning bolts.

Hair Club for Van Der Graaf Machines and Einstein Hair

This is the third post on Van Der Graaf demonstrations, and serves as an important theory point before you discuss charge distribution in hollow objects and air discharge and lightning rods.

Van Der Graaf Demonstrations - Induced Charge

It's demonstrations like this that really show the limits of Inductive-only learning in Science. Don't get me wrong, inductive teaching is a powerful tool under certain circumstances, but how the hell do you design an activity to inductively derive all the complexities of induced charge? Even if you can come up with one, it won't have as much impact or be as quick to do as the mixed-method demonstration discussed below.

Van Der Graaf Machines - Air Discharge and Identified Flying Objects

This is the last post I have on Van Der Graaf machines for the moment.
In this post, I describe demonstrations that show the charge on objects is restricted to the surface of the object, and objects with large radii, can store more charge than objects with small radii.

This explains why the Van Der Graaf machine has a large hollow sphere, and why dust (and the Hair Extension) reduces the charge on a Van Der Graaf machine.

Pearson's Square - Or Why Didn't My Chemistry Lecturers Teach Me This?

A common problem in chemistry (and feedlots, and home distilling, etc),

You have two solutions of different concentrations, let's call them H (high concentration) and L (low concentration), and you want to mix them to create a solution of concentration F (final concentration).

Using algebra, it takes a bit of time to get this.
xH + (1-x)L = C, etc, etc, etc, solve for x.

Using the Pearson's Square, it goes like this:

H - F = parts of solution L
F - L = parts of solution H