Electric Current

Electric CurrentElectric Current is the 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.

Measuring CurrentCurrent 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.

One ampere of charge in a circuit means that 6.2 x 1018 electrons pass a particular point every second.

When you connect an ammeter or voltmeter to a circuit, they must be on the right terminals.

-There are two terminals on a meter that you use to connect to a circuit.

The negative (–) terminal is often black, The positive (+) terminal is often red.

Always connect the positive terminal of the meter to the positive terminal of the electrical source.

Connect the negative terminal of the meter to the negative terminal of the electrical source.

Calculating Current

I

Q

t

Rearranging formulas- The magic triangle

I Q t

I

Q

t

Therefore, Amperes = Coulombs / s

Quantity Symbol Units of measurement

Charge Q C (coulomb)

Current I A (amperes) amps

Time t s (seconds)

GRASP Method to solving Problems G – Given - Write down the values that are

given to you in the problem R – Required – Write down the value that

you are trying to find. A - Analyze – Write down the formula that

you are going to useS – Solve – Substitute the given values into

the formulaP – Paraphrase – A statement that answers

the question

Example 1If 310 C of charge passes a point in a

conductor in 10 minutes, what is the current through that point in the conductor?

Given Charge = Q = 310 CTime =

Solve

= 0.52 ARequired Current = ? Paraphrase Therefore, the current is

0.52 amperes.

Analysis

Practice1. What amount of charge passes through a 3.0 amp

television in 1.3 hours? 2. What current does a stereo receiver draw if used for 2

minutes and goes through 10 coulombs of charge? 3. How long can a flashlight run for if it draws 0.11 amps and

its battery contains 10 coulombs of charge?4. If 15 coulombs of charge pass through a light bulb in 5

minutes, what amount of current passes through the bulb? 5. An ipod runs for 8 hours while drawing 0.05 amps of

current, how many coulombs of charge does the ipod contain?

6. A student leaves a 5 amp stereo on in their car and drains the 10000 coulomb battery. How long did the stereo stay on for?