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# Introduction to Magnetism

"Physics Is Imagination In A Straight Jacket"
John Moffat

- As we will see shortly, Electricity and Magnetism are different aspects of the same basic physical phenomenon - hence the description Electromagnetism.

- However, initially it is convenient to treat magnetism in a separate, but similar, manner to electricity. In other words we will define, magnetic forces, magnetic fields and magnetic dipoles exactly as we did the electric variables.

- After this initial description we will develop the relationship between magnetism and electricity through Faraday's Law of Induction and the Displacement Current, leading finally to a complete description of (classical) electromagnetism in the form of Maxwell's equations.

- So our starting point in describing magnetism will be the assumption of the existence of a magnetic field, B, the origin of which will be described later.

- Exactly as for the electric field E, we will assume that the B field can be represented by field lines where,

- the tangent to a field line gives the direction of B at that point and

- the number of field lines per unit cross sectional area is proportional to the strength of B.

- It is important to realize immediately that unlike electric field lines, magnetic field lines DO NOT represent the direction of the force acting on a charged particle.

> The magnetic phenomenon most familiar to most people is that of permanent magnetism - refrigerator magnets etc. As it happens, permanent magnetism is not a simple topic to explain. In fact a complete description requires a detailed knowledge of the quantum behavior of materials. For this reason we will barely mention permanent magnets in this course.

Q: What is the name of the first electricity detective?
A: Sherlock Ohms

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu