Post on 31-Dec-2015
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16-7 The Electric Field
• The idea that forces act over a distance and don’t have to be in contact was hard to understand
• Michael Faraday developed the idea of a Field
• The electric field extends outward from every charge
• If there is a second electric field placed near the first it feels the force of the first field
• The electric field at a point, P, has to consider both electric fields
• To do this consider a small positive test charge and determine how the electric fields effect the test charge
• The electric field, E is defined in terms of the force, F exerted on a tiny positive test charge, +q
q
FE
Units of N/C
• The electric field at any point in space can be measured
22
2
4
1/
r
Q
r
Qk
q
rkqQ
q
FE
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16-8 Field Lines
• The electric field is a vector, it is sometimes referred to as a vector field
• The electric field line or lines of force indicate the direction of the electric field at various points in space
• They are drawn indicating the direction of a force due to the given field on a positive test charge
• The number of lines starting on a positive charge or ending on a negative charge is proportional to the magnitude of the charge
• 1. Electric field lines indicate the direction of the electric field
• 2. The number of lines is proportional to the magnitude of the field
• 3. The electric field lines start on a positive charge and end on a negative charge
• The lines never cross, why not?
16-9 Electric Fields & Conductors
• The electric field inside a conductor is zero• The net charge on a conductor distributes
itself on the surface• The electric field is always perpendicular to
the surface outside of a conductor