17-3 Electric Fields

- A field is a region of space in which a ccertain quantity has a definite value at every point.

Examples of common fields are gravitational fields, electric fields, and magnetic fields.

- The electric field around a fixed charge Q is:

E = F_e / Q_o or E= k Q/r²

- The electric field is measured in N/C.

- When more than one charge contributes to the electric field, the net field E is the vector sum of the field contributions from the individual charges.

- Electric field lines provide a way for uss to visualize the electric field surrounding a charge or a system of charges.

- Three rules for drawing electric field lines are:

1. ) Electric field lines leave positive charges, and enter negative charges.
2. ) The density of the electric field lines is proportional to the magnitude of the field strength.
3. ) Field lines from the same field can not cross each other

- Although electric field lines do not actuually exist, they help us to more completely understand the concept of fields.

- The electric field is radially outward frrom positive charges, and radially inward on negative charges. Field lines never intersect.

- In the case of a charged metal object:

1. ) Inside the object the electric field is everywhere zero.
2. ) All excess charges reside on its surface.
3. ) The electric field is perpendicular to the object's surface.
4. ) On irregularly shaped conductors charges tend to accumulate at sharp points.