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Today4/28
Lab:
Electromagnetic
Induction
Last one!
Final Exam Topics
waves
interference
refraction
lenses/mirrors
E-Fields
potential
plates
capacitance
circuits
B-fields
Final Exam
Tuesday, 5/13, 10:15am Witmer 116
Problems pulled from
Lecture
HW
exams
We will cover a small amount of new
material as we review. New material
will be details of old material.
Motional EMF
Pos. charges cannot move, Neg.
charges shift down.
B
Rod has net pos at top and net neg
at bottom.
v
Rod becomes a battery with a V = EMF
Motional EMF
If in a circuit, current will flow.
B
V = IR etc.
v
Careful, only the rod can move.
Why?
Right-hand wire would also have an
EMF (opposing).
Motional EMF
How big is EMF?
B
v
Depends on:
B-field
Velocity
Length of rod
EMF = vBL when v, L, and B all
90°.
Units of Volts (or J/Coul)
Motional EMF
Problem solving.
B
Energy conservation!
Work done on bar = energy
dissipated in the resistor
v
Newton’s laws!
Force on the bar is balanced if at
constant speed (Force of the
external agent = mag. Force, IlB.
Motional EMF
What is the force on the bar by the
rope if it is pulled at constant a
speed of 2m/s through a 3T field?
The bar is 0.5m long and the
resistor is 5.
B
v
Frictionless
conducting rails