Ch. 21 - ElectricityCh. 21 -

ElectricityII. Electric CurrentII. Electric Current

Cell and BatteryPotential DifferenceCurrentResistanceOhm’s Law

A. Cell and BatteryA. Cell and BatteryCell

a device that produces an electric current by converting chemical energy into electrical energy

A cell conducts a current

Battery made up of many cells and also converts

chemical energy into electrical energy

C. CurrentC. Current

Current flow of electrons through a conductor depends on # of electrons passing a

point in a given time measured in amperes (A)

D. ResistanceD. Resistance

Resistance opposition to the flow of electrons electrical energy is converted to

thermal energy & light measured in ohms ()

Copper - low resistance Tungsten - high resistance

D. ResistanceD. ResistanceResistance depends on…

the conductor• good conductors have

low resistance wire thickness

• less resistance in thicker wires

wire length • less resistance in shorter wires

temp - less resistance at low temps

E. Ohm’s LawE. Ohm’s Law

Ohm’s Law

V = I × RV: potential difference (V)

I: current (A)

R: resistance ()

• Voltage increases when current increases.• Voltage decreases when resistance increases.

E. Ohm’s LawE. Ohm’s LawA lightbulb with a resistance of 160 is

plugged into a 120-V outlet. What is the current flowing through the bulb?

GIVEN:

R = 160 V = 120 V

I = ?

WORK:

I = V ÷ R

I = (120 V) ÷ (160 )

I = 0.75 A

I

V

R