10.9: Electric Current

Electric Current• Electric Current is the flow of electrons• it is a measure of the rate of electron flow past a given point

in a circuit• measured in amperes (A)

• Think of it in terms of a waterfall. If you could count the number of water molecules that drop over the edge every second, you could get the rate at which water is flowing past a particular point.

• Now think of the water molecules as electrons in a wire running past a particular point in a specific amount of time and you have the concept of current.

Electric Current

Electric Current

• Direct Current (DC)• flows in only one direction (electrons from a battery)

• Alternating Current (AC)• flows back and forth at regular intervals (comes from generators and carried to your home through power lines)

Electric Current – two types

DC Direct Current

AC Alternating Current

Current can KILL !

Measuring Current• Current in a circuit is measured using an ammeter. • The unit of electric current is the ampere (A). • An ampere is a measure of the amount of charge

moving past a point in the circuit every second.

Measuring Current• A current of 1 ampere means that 6.2 x 1018

electrons pass a particular point every second.

Ammeter• There are two terminals on the ammeter• The negative (–) terminal is often black, • The positive (+) terminal is often red.

Ammeter• Always connect the positive terminal of the meter closest

to the positive terminal of the electrical source (battery). • Connect the negative terminal of the meter closest to the

negative terminal of the electrical source.

Measuring Current Activity• Fill in the following table as you follow the steps

below

Connection of Ammeter Electric Current (A)Between light bulb and switch

Between battery and light bulb

Between battery and switch

Construct a circuit using a battery, light bulb, switch, and wires Connect the ammeter between the light bulb and switch Close the switch and note the current in the table Repeat the previous three steps after changing the position of the

ammeter, as described in the table

Follow-up• Does the current reading change if the ammeter is

moved to a different position in the circuit?

• No!• As long as the switch is closed, the current

should be consistent throughout the circuit.

Homework• Read pg. 314 - 315• Answer # 1 – 6 on pg. 315