Ch9 - electric fields
description
Transcript of Ch9 - electric fields
Force Types: : Contact & Non-contact Contact: Must touch such as friction or using a rope.Non-contact
Michael Faraday (British: 1791-1867)
Field area around an object that affects other similar objects
Test charge charge that’s in an electric field
Planet
Satellite Proton
Electron
Satellite & electron experience field forces
•Gravitational field by Newton
•Electric field by Faraday
•Non-contact–Remember gravity?2
typ
es o
f Fo
rces
r2
MGF =
ma
•What is the field?
•a (or g)a
r2
MG=
•Non-contact–Remember gravity?–What’s the field for a charge?2
typ
es o
f Fo
rces
F = ma
•What is the field?
•a (or g)
r2
QkF =
qE
•What is the field?
•Ea
r2
MG= E
r2
Qk=
2 ty
pes o
f Fo
rces
F =Eq F = force on test charge
q = charge of test charge
E = Electric Field (N/C)Q creates the
field
Two equations for electric fields
Er2
Qk=
Ele
ctric Field
Lin
es
•Drawing Electric field lines–Rules
•lines tell direction a + test charge will go
•Out of (away from) positiveInto (toward) negative
•Lines always come out the object perpendicular to the surface.
•more lines = stronger field.+ --
+ -
+ +
Sam
ple
Pro
ble
ms
•What is the electric field intensity of a 16 μC particle 5 cm away from the charge?
Er
2
Qk=
E0.05
2
(16x10-
6)(9x109)=
E=5.75x107 N/C
Pro
pertie
s of
cond
ucto
rs in
ele
ctrosta
tic eq
uilib
rium
1. Excess charges gather only on the outside of the surface, never inside.
2. The electric field is zero everywhere inside the conductor.
3. Electric field coming in or out of the conductor is perpendicular to the surface.
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E = 0 N/C
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--
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4. On an irregularly shaped surface, the charge will accumulate more where the radius of curvature is smallest.
This happens because the electrons will repel each other until they reach equilibrium.
Grounding An easy path for e’s to flow to or from
an infinite reservoir of e’s. Usually from the Earth to the electrical object.