Electric fields arise from charged objects and can exert forces on other charged objects. There are two types of electric charge: positive and negative. Electric field lines show the direction that a positive test charge would move due to the electric field. Electric fields are generated by both positive and negative charges, and the strength of the electric field depends on the magnitude of the charges and the distance between them, as described by Coulomb's law. The electric field strength is defined as the force per unit charge exerted by the field on a small test charge placed within it.

1. 6.2 – Electric Force and Field

2. Electric Forces simulations
Unlike Gravitational Fields with only one type of mass to act upon, Electric Fields
have two types of charge that they can make an Electric Force on: POSITIVE and
NEGATIVE.
http://phet.colorado.edu/en/simulation/travoltage http://phet.colorado.edu/en/simulation/balloons
or CLICK ON THE PICTURE or CLICK ON THE PICTURE
Use these two simulations to see how electric charges behave.
Notice which one can move and which one can’t?

3. Charges (Q) – measured in Coulombs
The Law of Conservation of Charge (Q)
Charge can neither be created nor destroyed.

4. Electric Fields
An electric field is a region of space
where a charged object experiences
a force due to its charge.
Field Lines
Because there are two charges that move in different directions in a field it has been
decided that Field Lines should show the direction that a POSITIVE charge would
accelerate if placed in the field.

5. Electric Fields (more examples)
The arrows are
always showing the
direction that a
POSITIVE charge
would move in the
field.

6. Electric Fields simulations
Charges and Fields Electric Field Hockey
http://phet.colorado.edu/sims/charges http://phet.colorado.edu/en/simulation/
-and-fields/charges-and-fields_en.html electric-hockey
Use these two simulations to see how the field lines work for different
charges.

7. Coulomb’s Law Newton’s Law
The Force between two point The Force between two point
charges is directly proportional to masses is directly proportional to
the product of the CHARGES and the product of the MASSES and
inversely proportional to the inversely proportional to the
square of their distance apart. square of their distance apart.
k= 9 x 10-9 Nm2C-2 G= 6.6742 x 10-11 m3kg-1s-2

8. Electric Field Gravitational Field
Strength Strength
Definition: Definition:
The force per unit charge The force per unit mass
experienced by a small positive experienced by a small test mass
test charge placed in the field. placed in the field.
Units: NC-1 Units: NKg-1
Example:

9. Electric Field around a sphere of charge Q
Because Field Strength is a vector it can be added using
Vector addition just like Gravitational Field Strength