1. Electric Fields and Electric Potential
SPH4U

2. Fields
Field: a region surrounding an object in which a force exists that will affect certain objects in that region Objects with mass generate gravitational fields. Objects with charge generate electric fields.

3. Electric Field Lines
Electric field lines indicate the direction and strength of the field at any point in the region.

4. Electric Field Lines
The direction is the direction of the force vector on a positive charge. The arrows therefore always point away from positive charges and toward negative charges.

5. Electric Field Lines
The direction is the direction of the force vector on a positive charge. The arrows therefore always point away from positive charges and toward negative charges.

6. Electric Field Lines
The strength is indicated by the density of the lines.
The field is stronger in here
than out here

7. e
Electric Field Strength (or Intensity) is the electric force per +1 C unit charge:
It has units of N/C (or V/m).

8. e
Electric Field Strength (or Intensity) is the electric force per +1 C unit charge:
It has units of N/C (or V/m).

9. e for a Point Charge
So if a point charge of q2 is placed in the field generated by a point charge of q1:

10. e for a Point Charge
So if a point charge of q2 is placed in the field generated by a point charge of q1:

11. e for a Point Charge
So if a point charge of q2 is placed in the field generated by a point charge of q1:

12. Parallel Plates
Between two charged parallel plates, the field between the plates is constant, with field lines equally spaced and perpendicular to the plates.

13. Parallel Plates
Between two charged parallel plates, the field between the plates is constant, with field lines equally spaced and perpendicular to the plates.
The strength of the field depends only on the charge/unit area on the plates.

14. Parallel Plates
(The field outside the plates is zero, other than a slight “bulging” distortion on the end.)

15. Parallel Plates
(The field outside the plates is zero, other than a slight “bulging” distortion on the end.)
constant e
So force is also constant:

16. Electric Potential Energy
Recall that

17. Electric Potential Energy
Recall that So

18. Electric Potential Energy
Recall that So
Where’s the negative?
In the signs of the charges.

19. Electric Potential Energy
Note that Ee is negative for opposite charges that attract and positive for like charges that repel.

20. Electric Potential
Electric Potential is the is the energy per +1 C unit charge:
It has units of J/C or Volts.

21. Electric Potential
Electric Potential is the is the energy per +1 C unit charge:
It has units of J/C or Volts.

22. Electric Potential Difference
Consider a positive point charge q being moved from position A to position B in a uniform electric field:

23. Electric Potential Difference
Consider a positive point charge q being moved from position A to position B in a uniform electric field:
DV is the potential difference.

24. Electric Potential Difference
Also:
where Dd is the straight-line distance parallel to the field

25. Electric Potential Difference
Also:
where Dd is the straight-line distance parallel to the field
(If we are moving the charge from one plate to another,
Dd is the plate separation.)

26. Electric Potential Difference

27. Electric Potential Difference
voltage across the plates
separation between the plates

28. Electric Potential Difference
Note the units:
1 V/m = 1 N/C

29. More Practice “pHet Electric Field Simulation Activity”
Textbook Questions
p. 343 #1, 2, 3, 4
p. 354 #1, 2, 3
p. 356 Practice #6