5-Magnetism

Slideshow:  Magnetism

Textbook: Chapters 17 & 18

Right Hand Rule Practice: http://www.cstephenmurray.com

Objectives: 

• Magnet structure

  • explain magnetic domains in ferromagnets (permanent) compared to paramagnetic materials (weak & temporary) in terms of number of domains aligned and amount of alignment. 

  • dipole is backwards from field line direction.

  • why no monopoles?

• Magnets in fields

  • explain dipole alignment of a magnet in a field (example: compasses & earth as a dipole)

  • Explain metal filings & paper clips as induced dipoles

• magnetic force on a charged particles/objects

  • Use the right hand rule and F = qvB to solve and explain problems 

  • including 0º, 90º and 180º degree angles of v to field, but discuss effect at other angles

• magnetic force created by a current carrying wire

  • Use grabbing right hand rule to find B fields tangential to concentric circles at specific points

  • compare strength of field at distances from the wire

  • Use B=(u/2pi)(I/r)

• Electromagnetic Induction

  • Magnetic flux is kind of like magnetic field density (#lines passing through and area), but is mathematically B(cosθ)A

    • Changing flux induces an electric field  

    • if there are charges (like in a wire), the E field created by the changing flux cancause a current. according to ɛ= –ΔB/t, where the negative sign indicates the EMF opposes the change in flux.

    • conservation of energy applies to magnetic forces

• summary: 4 ways to cause a magnetic force

  • 2 magnets

  • 1 magnet with charged particle(s) moving nearby

  • 1 magnet moving near charged particle(s)

  • multiple charged moving objects (ex. 2 wires carrying current, straight or in loops)

Common Misconceptions:

Fields

• Misconception: North and south magnetic poles are the same as positive and negative charges.

  • Correct Principle: Magnetism and electric charge interactions are separate (although they can influence each other). Magnets are caused by a magnetic dipole based on spin , which will always have a N and S side, where electric charge interactions are based on the intrinsic properties of a particle. You can have single charges isolated from their opposite, but not single magnetic poles. 

• Misconception: Poles can be isolated.

• Misconception: Flux is the same as field lines.

• Misconception: Flux is actually the flow of the magnetic field.

• Misconception: Magnetic fields are the same as electric fields.

• Misconception: Charges at rest can experience magnetic forces.

• Misconception: Magnetic fields from magnets are not caused by moving charges.

• Misconception: Magnetic fields are not 3-dimensional.

• Misconception: Magnetic field lines hold you on the Earth.

• Misconception: Charges, when released, will move toward the poles of a magnet.

• Misconception: Magnetic field lines start at one pole and end at the other.

Induction

• Misconception: Generating electricity requires no work.

• Misconception: When generating electricity only the magnet can move.

• Misconception: Voltage can only be induced in a closed circuit.

• Misconception: Magnetic flux, rather than change of magnetic flux, causes an induced emf.

• Misconception: All electric fields must start on (+) and end on (-) charges.

• Misconception: Water in dams causes electricity.

To Be Continued . . .