Electricity

1
Electricity Magnetism

• Unit I - Charge Behavior and Interactions
• Charge produces and responds to an electric field
• Unit II - Electric Potential
• An electric field can store energy
• Unit III - Circuits
• The electric field can cause bulk charge flow in
  conducting materials
• Unit IV - Magnetism
• Charge flow produces and responds to a new field

2
Whats the same?

• Many of the labs and activities are very familiar
• Sticky tape, Coulombs Law
• Mapping electric potential
• Ohms Law, resistance in series and parallel
• Mapping magnetic field
• Many of the exercises are familiar

3
So, whats different?

• Develop models to account for observed phenomena
• Use these models throughout the entire set of
  materials
• Diagrammatic representations, causal mechanisms
  stressed over QPS using plug-n-chug approach

4
I- Charge and Field

• Emphasis on atomic model of matter
• charge is a fundamental property of matter (like
  mass)
• charge carriers are microscopic constituents of
  matter
• behavior of charged objects results from uneven
  charge distribution

5
I- Charge and Field

• Compare and contrast electrical and gravitational
  forces
• force arises from fundamental property of objects
  (mass vs charge)
• inverse square relationships between point
  particles
• differences in magnitude and direction

6
I - Charge Field

• Emphasis placed on origin and nature of the field
• arises from uneven distribution of charge
• strength is the force per unit something
• mediates the force between charges
• stores energy due to interactions

7
II - Potential Energy

• Continue analogy with gravitational field
• Relate electric equipotentials to contour lines
  on a topographic map

8
II - Potential Energy

• Continue analogy with gravitational field
• Relate electric equipotentials to contour lines
  on a topographic map
• Potential is property of position in field
• Changes in potential energy depend on field
  strength, change in position and a property of
  the object

9
II - Potential Energy

• Formulas are developed in context of energy
  storage and transfer

10
II - Potential Energy

• Formulas are developed in context of energy
  storage and transfer
• Rearrangement yields essential relationships

11
III - Circuits

• Emphasis on causal mechanisms rather than
  application of Ohms and Kirchoffs Laws
• field responsible for bulk flow of charge in
  conductors
• ?V accounted for by differences in charge density
• Study of circuits no longer disconnected from
  field and potential developed earlier

12
III - Circuits

• Influences
• Sherwood and Chabay article
• A Unified Treatment of Electrostatics and
  Circuits
• surface charge distribution responsible for field
• CASTLE curriculum
• unequal initial flow rates can cause compression
  or depletion of charge

13
III - Circuits

• Paradigm labs examine whats happening in the
  wires as well as in resistors
• use voltage probe to measure ?V in wire during
  transient
• make charge distribution maps to account for ?V
• infer existence of field
• must also exist in wires if charge is to flow
• field strength dependent on charge distributions

14
III - Circuits

• Sketch the charge distribution and field in the
  intervals midway through the discharge of the
  capacitor through the long bulb.
• Sketch a diagram that you feel describes the
  charge distribution, wire size and field midway
  through the discharge of the capacitor through
  the round bulb. In what ways are the diagrams
  similar? How are they different?

15
IV - Magnetism

• Moving charge produces and responds to a magnetic
  field
• 1st lab - mapping field produced by charge moving
  in a wire
• RH curl rule
• field strength increases with current and
  decreases with distance

16
IV - Magnetism

• Compare/contrast with electric field
• E-field - static charge, lines originate from ()
  and terminate on (-)
• B-field - moving charge, lines form closed loops
• Magnetic domains in permanent magnets result of
  electron spin

17
IV - Magnetism

• Demo to show how force acts on wire carrying
  current.
• Mr BIls swing is deflectedout from magnetic
  fieldwhen current runs throughthe wire
• RH palm rule
• Sets up lab with current balance

18
IV - Magnetism

• Small motor projectapplication of Lorentzforce
  on loop
• Loop rotates to alignB fields
• Sets stage for introduction of flux and
  induction

19
Materials are a work-in-progress

• Magnetism least well-developed of the EM units
• Instructional notes in all units need work to
  more coherently develop story line
• Feedback from Modeling teachers should help