Magnetism Introduction Section 0 Lecture 1 Slide 1 Lecture 32 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 32 Magnetism

Introduction Section 0 Lecture 1 Slide 2 Lecture 32 Slide 2 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet *Homework Handout

Magnetism Introduction Section 0 Lecture 1 Slide 3 Lecture 32 Slide 3 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Review Lecture 32 Magnetism

Introduction Section 0 Lecture 1 Slide 4 Lecture 32 Slide 4 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 What is the Earth’s magnetic field? Is the magnetic force similar to the electrostatic force? How do magnets work?

Magnetism Introduction Section 0 Lecture 1 Slide 5 Lecture 32 Slide 5 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Magnets and the Magnetic Force We are generally more familiar with magnetic forces than with electrostatic forces. Like the gravitational force and the electrostatic force, this force acts even when the objects are not touching one another. Is there a relationship between electrical effects and magnetism? Maxwell discovered that the electrostatic force and the magnetic force are really just different aspects of one fundamental electromagnetic force. Our understanding of that relationship has led to numerous inventions such as electric motors, electric generators, transformers, etc. James Clerk Maxwell

Magnetism Introduction Section 0 Lecture 1 Slide 6 Lecture 32 Slide 6 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Electromagnetic Waves Maxwell Equations (1865) described all of E&M. They predict the existence of EM waves: – c is speed of EM waves (light) Hetrz (1888) showed EM waves: – have speed c – have wavelength – have both E and M components – reflect – Refract – Interfere – diffract

Magnetism Introduction Section 0 Lecture 1 Slide 7 Lecture 32 Slide 7 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 The Basics Lecture 32 Magnetism

Introduction Section 0 Lecture 1 Slide 8 Lecture 32 Slide 8 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 As you probably already know, magnets attract metallic items made of iron or steel, but not silver, copper, aluminum, or most nonmetallic materials. –The three most common magnetic elements are the metals iron, cobalt, and nickel. Magnets also attract or repel each other depending on how they are aligned. –The north-seeking end of a magnet wants to point north, and it is called the north magnetic pole. –The south-seeking end wants to point south, and it is called the south magnetic pole. Like poles repel one another, and unlike poles attract one another. Magnets: The Basics

Magnetism Introduction Section 0 Lecture 1 Slide 9 Lecture 32 Slide 9 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The force that two poles exert on one another varies with distance or pole strength. –The magnetic force between two poles decreases with the square of the distance between the two poles, just as the electrostatic force does. –Some magnets are stronger than others; the force is directly proportional to the pole strength of the magnets involved. Magnetic Force: The Basics

Magnetism Introduction Section 0 Lecture 1 Slide 10 Lecture 32 Slide 10 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A magnet always has at least two poles: a magnetic dipole. –Breaking a magnetic dipole in half results in two smaller magnetic dipoles. –We cannot get just one magnetic north or south pole by itself: magnetic monopoles do not exist. Magnetic Fields: The Basics

Magnetism Introduction Section 0 Lecture 1 Slide 11 Lecture 32 Slide 11 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Magnetic field lines produced by a magnetic dipole form a pattern similar to the electric field lines produced by an electric dipole. –Electric field lines originate on positive charges and terminate on negative charges. –Magnetic field lines form continuous loops: they emerge from the north pole and enter through the south pole, pointing from the north pole to the south pole outside the magnet. –Inside the magnet, they point from the south pole to the north pole. Magnetic Fields: The Basics

Magnetism Introduction Section 0 Lecture 1 Slide 12 Lecture 32 Slide 12 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A magnetic dipole tends to line up with an externally produced magnetic field just as an electric dipole tends to line up with an electric field. –Both dipoles experience a torque due to the force from the externally produced field. –This is why iron filings line up with the field lines around a magnet. Interactions with Magnetic Fields

Magnetism Introduction Section 0 Lecture 1 Slide 13 Lecture 32 Slide 13 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 The Earth’s Magnetic Field Lecture 32 Magnetism

Introduction Section 0 Lecture 1 Slide 14 Lecture 32 Slide 14 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The north (north-seeking) pole of a compass needle points toward the Earth’s “North Pole.” Is the Earth a magnet? The magnetic field produced by the Earth can be pictured by imagining a large bar magnet inside the Earth. Since unlike poles attract, the south pole of the Earth’s magnet must point in a northerly direction. The axis of the Earth’s magnetic field is not aligned exactly with the Earth’s axis of rotation.

Magnetism Introduction Section 0 Lecture 1 Slide 15 Lecture 32 Slide 15 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The Earth’s magnetic fields are known to “flip” at irregular intervals. Flippin’ Cool (no wait hot…)

Magnetism Introduction Section 0 Lecture 1 Slide 16 Lecture 32 Slide 16 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Magnetism and Current Loops Lecture 32 Magnetism

Introduction Section 0 Lecture 1 Slide 17 Lecture 32 Slide 17 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Magnetic Effects of Electric Currents Oersted discovered that a compass needle was deflected by a current-carrying wire. –With the wire oriented along a north-south line, the compass needle deflects away from this line when there is current flowing in the wire.

Magnetism Introduction Section 0 Lecture 1 Slide 18 Lecture 32 Slide 18 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology Next Lab/Demo: Electric Circuits Magnetism Thursday 1:30-2:45 ESLC 46 Ch 13 and 14 Next Class: Friday 10:30-11:20 BUS 318 room Read Ch 14