Magnetism Intro. 1) Students will be able to describe the magnetic fields around bar magnets. 2) Students will be able to use a compass to determine the direction of a magnetic field. 1
Teachers' notes Subject Topic Title Physics 30 B06 Magnetism Intro Magnetism Intro Labs Handouts B06 Magnetism Intro Assignment 2
Lesson notes 3
Some key concepts: magnets have poles, not charges! All magnets have a North and a South pole. Rules governing magnets: opposite poles attract similar poles repel the direction of a magnetic field is the direction that the north end of a test magnet (i.e. a compass) points. 4
Activity: What kinds of materials do magnets attract? How can we turn a metal wire into a magnet? 5
Activity: What do the field lines around magnets look like? Directions: use a compass near the magnets to determine the direction of magnetic fields. Sketch you results. Now we'll use iron filings to show the magnetic field shapes. 6
Why did one metal become magnetized and the other didn't? 7
More magnetic field stuff... 8
Magnetic Fields and Moving Charges Hans Christian Oersted discoverd that current in a wire will cause a nearby compass to deflect. Electric current (i.e. moving charges) produce a circular magnetic field around a wire. 9
see p. 587 10
"Hand rules" are a visual way of predicting the direction of a magnetic field (or the effect of a field). For all the HR's, we use our left hand for negative charges and our right hand for positive charges. Electron flow is from the ( ) end of a voltage source to the (+). "Conventional current" is the direction that positive charge would move (+ to ) if positives could move in a solid (they can't!). 11
Current Carrying Wire Hand Rule (or the "grasp" rule): used to determine the magnetic field around a current carrying wire See p. 588 12
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How can we use the battery and the wire to increase the strength of the magnetic field? 15
We can increase the magnitude of the electric field (i.e. make an electromagnet) by wrapping the wire into loops to make a solenoid. 16
We can see that the magnetic field around each loop of the wire can be added together to make a stronger net field. 17
Solenoid Hand Rule (see p.588) 18
Current: a measure of the amount of charge flowing by a location in a specific time Current (Amperes, A) I = q t Charge (C) time (s) 19
The Motor Effect, F m A moving object that has a charge will experience a magnetic force when placed in a perpendicular external magnetic field. 20
How field interactions produce a magnetic force: 21
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Motor Effect Hand Rule (p. 595) 23
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Calculating the Magnetic Force: On a current carrying wire: F m = B I L Magnetic field strength Tesla (T) On a freely moving charge: Length of wire inside and to the field (m) F m = B qv 25
p. 605 26
Magnetic Force on Current Carrying Wire Lab 27
p. 599 28
Practice Questions: p. 601, #5 10 12.1 etest 12.2 etest 29
How can we communicate the use of the motor effect HR? e.g. In what direction will the wire experience a magnetic force? x x x x x x x x x x x x x x x x 30
Motor Effect Grade:«grade» Subject: Physics 30 Date:«date» 31
1 A B C 32
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Hand Rule Review: 34
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