1. IB 5.2 Electric Field & Potential

2. Electric Field
Just like mass create gravitational fields, charges create electric fields
With gravity the field strength is measure as Newton per kilogram
What do you think Electric fields are measured in?
Newton's per Coulomb

3. Measuring the Electric Field
If the unit is Newton's per Coulomb, what is the equation?
E = F / qo
Simple enough, right.
E = Electric Field
F = Force
qo = charge in the field

4. Summing electric Fields
Alternative Equation:
It is the surrounding charges that creates an electric field at a given point in space.
Look at Example 8

5. Picturing the Electric Field
Click on the picture to open an applet

6. Electric Field Rules
Fields start at positive and end at negative, or start and end at infinity.
This is by convention. The field is said to predict the movement of a positive charge.
The density of lines should represent the strength of the field.
A positive charge will have a velocity tangent to a field line.
Field lines do not actually exist since the are an infinite number of paths a test charge can take.

7. Parallel Plate Capacitors
Used to store charge.
The most common type is a parallel plate capacitor.
Charge is spread uniformly, not really, throughout the plate
The electric field between two parallel plates is 100 N C-1.
What acceleration would a 2.0 mC charge with a mass of 10-3 kg experience if placed in the field?

8. Electric Potential Consider a positive charge Q and a test charge q.
Work must be done to move q closer to Q since like charges repel.
V = Voltage (Potential measured in Volts)

9. Work and Route
Regardless of the path taken to move the charge the work is always the same.
Electric Potential Energy is U = qV
Potential Difference is DU

10. Electric Fields Inside Conductors
Excess electric charge moves to the surface of a conductor
At equilibrium the electric field inside a conductor is zero
This comes from the fact that free electrons will always be on the outside of the conductor.
So the electric field lines don’t penetrate the conductor
The electric field outside a conductor is perpendicular to the surface
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