Electric Current Lesson 8 December 9th, 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 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 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 Q t Rearranging formulas - The magic triangle 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 use S – Solve – Substitute the given values into the formula P – Paraphrase – A statement that answers the question

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 = 0.52 A Required Current = ? Paraphrase Therefore, the current is 0.52 amperes. Analysis

Example 2 A 6.5 amp vacuum cleaner is used for 34 minutes, how much charge would pass through the vacuum during this time? G Current = I = 6.5 amp Time = S Q = 13260 Coulombs R Charge = Q = ? P Therefore, the 13260 Cof charge would pass through the vacuum cleaner in 34 minutes. A

Example 3 G I = 5.3 A Q = 20 C S t = 3.77 s R t = ? P 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 t = 3.77 s R t = ? P Therefore the drill was used for 3.77 seconds. A

Practice 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?