SPH3U: Electricity Electric Current & Circuits

Electric Current A conductor is an object that lets electrons move freely. An electric current is defined as the number of electrons moving in the same direction past a certain point in one second. The symbol for electric current is I.

Electric Current Imagine a wire (Figure 3) of known cross- sectional area, with a total charge Q (in coulombs) flowing through the area A in a time Δt (in seconds). Then the electric current I through the wire is:

Electric Current The electric current I through the wire is:

Electric Current Which way does the electricity actually move in the wire? The answer depends on whether you are using a Conventional Current model or an Electron flow model. The Conventional Current model was used first, and still tends to be more widely used today, despite being technically wrong.

Electric Current Most texts and physicists use conventional notation

Electric Current Electrons actually move from the negative terminal to the positive.

Electric Current Electric current is measured in units called Amperes (A). 1 Ampere = (1 Coulomb / second ) The electric current supplied by a battery is very different from the electric current that comes from a wall.

Electric Current  Batteries supply direct current (DC)  Wall sockets supply alternating current (AC).  The direct current supplied by a battery is in a fixed single direction and it doesn’t increase or decrease in magnitude.  the alternating current supplied by a wall socket periodically reverses direction in the circuit and the amount of current varies continuously.

Measuring Electric Current An Ammeter is a device that measures the amount of electric current in a circuit. It is connected directly into the path of the moving charges. This type of connection is called a series connection.

Measuring Electric Current Ammeters are connected in series in the circuit.

Example Question 1 What is the current if 3 Coulombs of charge pass a point in 2.8 seconds?

Example Question 1 What is the current if 3 Coulombs of charge pass a point in 2.8 seconds? Answer:

Example Question 2 If a battery can produce a charge of 3000mA for 1 hour before it is depleted, for how long could it produce a current of 2000mA?

Example Question 2 If a battery can produce a charge of 3000mA for 1 hour before it is depleted, for how long could it produce a current of 2000mA? Answer: 3000mA = 3A 1 hour = 3600 seconds I = Q/t  Q = (I)(t) = (3)(3600) = C 2000mA = 2A I = Q/t  t = Q/I = 10800C / 2 = 5400 seconds = 1.5 hours

Basics of Circuits Circuits are continuous paths in which electric current can flow. A circuit can be composed of various components. Some typical components of electric circuits are sources (where the power comes from), loads (things that use the energy), resistors, capacitors, wires, and switches.

Basics of Circuits Circuit PartFunction Battery (cell) Source of electric energy WiresProvide a path for the electrons to travel on. Resistor or load Uses up the energy – often dissipates it as heat. VoltmeterMeasure electric potential difference AmmeterMeasure electric current

Basics of Circuits Circuits need to consist of a closed loop in which the electric charge can continuously move. If there is a break in the path, the electrons will cease to flow.

Basics of Circuits

Circuits are classified as either parallel or in series depending on how they are connected.

Basics of Circuits When a circuit is connected in series, there is only one way the electrons can go. When a circuit is connected in parallel, there is more than one way the electrons can go.

Basics of Circuits A “short circuit” happens when electricity is allowed to move through a path of least resistance, in essence, not using up any energy.

Videos Circuit basics nVkCkX4 nVkCkX4 How electrons move in a circuit TPSXk TPSXk

Homework Read section 11.5 in your text. Answer questions 1-5 page. 518