Lesson 8 December 9 th , 2011

 Electric 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 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.

 One ampere of charge in a circuit means that

6.2 x 10 18

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

I

Rearranging formulas - The magic triangle

t I Q t Q Therefore, Amperes = Coulombs / s

Quantity

Charge Current Time

Symbol Q I t Units of measurement C (coulomb) A (amperes) amps s (seconds)

GRASP Method to solving Problems



G – Given

- Write down the values that are given to you in the problem 

R – Required

trying to find. – Write down the value that you are 

A Analyze

going to use – Write down the formula that you are 

S – Solve

formula – Substitute the given values into the 

P – Paraphrase

question – A statement that answers the

Example 1

 If 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 C Time = Solve Required Current = ?

= 0.52 A Paraphrase Therefore, the current is 0.52 amperes.

Analysis

Example 2

G  A 6.5 amp vacuum cleaner is used for 34 minutes, how much charge would pass through the vacuum during this time?

Current = I = 6.5 amp Time = S Q = 13260 Coulombs R Charge = Q = ?

A P Therefore, the 13260 Cof charge would pass through the vacuum cleaner in 34 minutes.

Example 3

 A a 5.3 amp drill has 20 coulombs of charge pass through it, how long was the drill used for?

G I = 5.3 A Q = 20 C S R t = ?

t = 3.77 s P Therefore the drill was used for 3.77 seconds. A

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Practice

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What amount of charge passes through a 3.0 amp television in 1.3 hours? What current does a stereo receiver draw if used for 2 minutes and goes through 10 coulombs of charge? How long can a flashlight run for if it draws 0.11 amps and its battery contains 10 coulombs of charge?

If 15 coulombs of charge pass through a light bulb in 5 minutes, what amount of current passes through the bulb? An ipod runs for 8 hours while drawing 0.05 amps of current, how many coulombs of charge does the ipod contain? 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?