Electric field and forces
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Transcript of Electric field and forces
![Page 1: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/1.jpg)
Do you have access to MasteringPhysics
A) Yes B) No C) No, but I am confident
to get it from the bookstore before Thursday January 23
Clicker question
![Page 2: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/2.jpg)
Electric field and forces
Let’s reconsider Coulomb interaction
We know already
20
00 4
1
r
qqF A
We ask:How does particle B know that A is there to exert a force
Answer:The presence of charge A alters the empty space and charge B experiences this alteration we call electric field
Point P
0
0
q
FE
and vice versa
![Page 3: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/3.jpg)
Point P
0
0
q
FE
EqF 00
The concept of probing the electric field by the force experienced by a test charge gives rise to the definition:
The electric field E at a given point is given by the force F0
experienced by the test charge q0 divided by q0
0
0
00
limq
FE
q
A test charge q0 at point P experiences the force
The limit makes sure that the test charge does not affect the surrounding charge distribution
![Page 4: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/4.jpg)
q0
q
Vector properties of E originate from vector properties of F 0
0
0
00
limq
FE
q From we realize that the electric field is a vector quantity
Let’s first have a closer look to the vector properties of the Coulomb force
x
y
z 1r2r
2 1r r r F 0 points in the direction of
2 1r r r
00 2
0
1ˆ
4
q qF r
r
When writing:
ˆ :r
rr
where and
is a unit vector pointingin direction of
rEverything is taken care of, including the various signs of both charges
![Page 5: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/5.jpg)
With the full vector information about the force F0 the test charge experiences in an electric field of a point charge q we can visualize the vector character of the E-field of a point charge
00 2
0
1ˆ
4
q qF r
r
+q
20
1ˆ
4
qE r
r
E-field of a positive point charge:
x
y
z
q0
q0
![Page 6: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/6.jpg)
-q
E-field of a negative point charge:
is mathematically speaking a vector field( )E r
-Remember: for a 1-dimensional function we assign to every x a value f(x) -for a vector field in 3d we assign to every point in 3d space a vector
( , , )r x y z( ( , , ), ( , , ), ( , , ))x y zE E x y z E x y z E x y z
If 0( )E r E independent of (x,y,z) we say the field is homogeneous A special case is the zero electric field inside a
conductor Electrostatic fields must be zero here because otherwise they would drive a current
![Page 7: Electric field and forces](https://reader035.fdocuments.us/reader035/viewer/2022072015/5681306f550346895d965130/html5/thumbnails/7.jpg)
For the charge distribution shown in the figure indicate a region where a point exists at which the net electric field is zero
A) Region A
B) Region B
C) Point C
D) Region D
E) Region E
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