Chapter 33

Electric Fields

And

Potential

And

Ohm’s Law

Just as the space around Earth and every other mass is filled with a gravitational field, the space around every electric

charge is filled with an electric field.

http://www.amasci.com/emotor/bill3.jpg

Just as gravitational forces hold a satellite around the earth.

Electrical forces hold an electron in orbit around a nucleus.

Electric fieldThe area around a charged

object. This field exerts a force on any charged object in its

vicinity. The closer the charged object is brought to the charged

object creating the field, the greater the force exerted on it.

An electric field has magnitude and direction. So it is a …….

Vector

Its magnitude (strength) can be measured by its effect on

charges located in the field.

Electric field linesThe electric field can be

represented with electric field lines. The closer the lines are,

the stronger the field is.

electric field lines point in the direction which a positive test

charge would accelerate if placed upon the line.

Field lines are always directed from the positive charge and toward a negative charge.

Electric Potential Energy:The energy a charge possesses

by virtue of its location

Electric Potential work done on a charge; or the

electric potential is the potential energy per unit charge

(symbol is V; SI unit is volt)

Electric Potential = Electrical potential energy /

charge

Potential = work / test charge

or

V = W / qo

Remember, the term “work” can be replaced with the term “energy” because to store

energy in, or to give energy to, an object, work must be done.

1 volt = 1 Joule / coulomb

Capacitora device that stores charge in the electric field between its

plates. Each plate carries the same amount of charge, one plate being negative and the

other being positive. A potential difference exists between the

two plates.

Capacitors are found in almost all electronic circuits

Ohm’s Law

Georg Simon Ohm discovered that the current in a circuit is directly proportional to the

voltage impressed across the circuit and is inversely

proportional to the resistance of the circuit

Current = voltage / resistance

I = V / R

Current (I) – amperesPotential Difference (V) – volts

Resistance (R) - ohms

Read page 525

Page 526 has pictures of different capacitors