April27A_day26.notebook
April 27, 2012
Check for Understanding
Potential difference = 10V
Negative
1. Draw the electric field lines between the charged plates
Positive
d = 4cm
2. How much work would be done moving 2 electrons across the potential toward the negative plate?
3. Calculate the electric field intensity between the plates
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April27A_day26.notebook
April 27, 2012
Before we go over the homework...
Equipotential Surfaces
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April27A_day26.notebook
April 27, 2012
Equipotential Surfaces
No work is required to move a charge at a constant speed along an equipotential surface (dotted line)
The electric field at every point along an equipotential surface is perpendicular to the surface
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April27A_day26.notebook
April 27, 2012
Capacitance
Capacitance is the ratio of charge on either conducting plate to magnitude of the potential difference between two conducting surfaces
Capacitors STORE charge
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April27A_day26.notebook
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http://hyperphysics.phy­astr.gsu.edu/hbase/electric/pplate.html
Practice
A parallel plate capacitor has an area of A = 2 X 10­4 m2 and a plate separation of 1 mm.
a) Find its capacitance
b) How much charge is stored on the positive plate if it is connected to a 3V battery?
c) Find the electric field intensity between the plates.
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April27A_day26.notebook
April 27, 2012
http://hyperphysics.phy­astr.gsu.edu/hbase/electric/pplate.html
Capacitors STORE electrical energy
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April27A_day26.notebook
April 27, 2012
HW P. 566 # 21, 25, & 26
21. for 100V d = 0.72m
for 50V d = 1.44m
for 25V d = 2.88m
25. a) C = 1.11 X 10­8F
b) Qmax = 26.55C
26. a) C = 2.43 X 10­4F
b) Q = 2.205 X 10­5 F
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