Introduce the background ideas of magnetism.
Reveal student conceptions/explanations of magnetic phenomena.
Student Learning Objectives:
Demonstrate the effect of one magnet on other magnets.
Demonstrate that attraction and repulsion are related to relative geometric orientation of the magnets and not external parameters.
Demonstrate that magnetic strength increases as separation decreases.
Demonstrate that certain types of materials in the environment, while not themselves magnetic, do interact with magnets.
Prepare packs of material for each group. Include in each pack:
Opening Discussion: (5-8 minutes)
Magnetism has been 'used' for several thousand years.
Magnetism has been understood by science for c. 150 years.
Magnetic objects exert a force on other magnetic objects and act in a particular direction.
Student Activities with Materials
Closing Class Discussion
Lead discussion that draws out the student observations made during activity.
Suggested Homework Assignments
Ask students to design a method for detecting a magnetic field.
(A possible hint is to remind them of the nature of Newton's Third Law: that which feels the force must also be able to exert the same force.)
Ask students to design a method for determining the strength of a magnet.
(Quite hard to do as you need a reference magnet of known strength. The method of choice is to use a current or a Hall Effect probe but students don't know this.)
Ask students to design a method to find the dependence between
separation of magnets and the force of interaction.
(Quite hard to do as assumptions about center of magnet coinciding with center of mass and rotational effects have a significant effect.)
Use Newton's Law to calculate the magnetic force of interaction on
a magnetic pendulum in the vicinity of a 2nd magnet. The students cannot
assume the magnetic force is completely horizontal. The following free body
diagram is suggested:
The smallest angle of B with the horizontal is gamma. The larger angle of T with the horizontal is theta. The weight (mg) is along the downward vertical. Find B(gamma,theta,W). Solve for the three cases gamma = 0°, gamma = 90°, gamma = theta.