# Magnetism Lab - University of Michigan

Physics 106 Lesson #19 Magnetism Dr. Andrew Tomasch 2405 Randall Lab [email protected] Review: Engineering Trade Studies When a number of possible engineering solutions exist to meet a given need or goal, engineers perform a trade study. This is a useful approach whenever a

choice is to be made between a number of possible options. The benefits, disadvantages and costs are quantified for each option and decisions are then made by trading off advantages against disadvantages for the various options based on a goal such as minimum cost, safety, or maximum reliability. Magnets All magnets have two

poles: North and South Like poles repel each other; Unlike poles attract each other Magnetic poles are always found in pairs Isolated magnetic poles have never been found Magnetic Forces

Electricity and Magnetism Originally thought to be independent phenomena Like gravity, both have actionat-a-distance force laws Faraday and others believed in the unity of nature Maxwell proved that they were both aspects of a single phenomenon: Michael Faraday

Electromagnetism James Clerk Maxwell The Magnetic Field The magnetic field is a vector and denoted by the letter B B The north pole of a

compass needle is a magnetic north pole The direction of the magnetic field at any point in space is the direction indicated by the north pole of a small compass needle (test magnet) placed at that point

Magnetic Field Lines Magnetic field lines surround magnets The magnetic field is always tangent to the magnetic field line The number of lines per unit area (density) is proportional to the magnetic field strength Outside of the magnet, magnetic field lines point

away from north poles and toward south poles B Iron Filings: Visualizing Magnetic Field Lines The magnetic field lines inside a bar magnet run from south pole to north pole.

The Earths Magnetic Field The Earth's magnetic field is similar to that of a bar magnet tilted 11 degrees from the spin axis of the Earth Caused by the dynamo effect, the rotation of a partially ionized outer core internal electric current! The north pole of a

compass needle is attracted to the geographic North Pole, which is therefore a magnetic south pole South magnetic pole Magnetic Field Produced by a Long, Straight Wire Demonstration: Oersted Experiment

Field Direction for a Straight Wire The magnetic field due to the current in a long straight wire has circular field lines around the wire The direction of the field is given by a right hand rule

Electromagnets Current flowing in a loop of wire creates a magnetic field The Current loop can be visualized as a phantom bar magnet N S =

N S Which End is the North Pole? Another Right Hand Rule! N S The Field of a Solenoid Current Into Page

B Current Out of Page Inside a solenoid (away from the ends) the magnetic field is constant.

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