2.2

Electric Circuits Recall: Terminal = electrode = +ve and –ve ends Metal component on cell that supplies electrons (-ve) or receives electrons (+ve) Must be connected to other components to complete a circuit Open circuit – has a gap or a break Electrons can’t flow

Electric Circuits There are 4 essential components of a circuit: 1. Source of electrical energy a. Generator – converts mechanical energy (motion) to electrical energy b. Cell – converts chemical energy to electrical energy c. Battery – 2 or more connected cells 2. Conducting wires a. Metal wires connect all parts of the circuit

Electric Circuits 3.Load/Resistor: Provides resistance to electron flow A device that transforms electrical energy to another type of energy a.Light bulb (lamp) b.Motor 4. Switch - a control device that completes or breaks the circuit a. Fuse or circuit breaker

Electric Current River current = the volume water that flows past a certain point in a specific time (m 3 /s) Fast current = more water per second Electric current = a measure of the number of electrons that flow past a point in a circuit every second Electrons are too numerous to count, so they are grouped into coulombs (C)

Electric Current Amount of electrons or “charges” = coulombs given the symbol “q” 1 coulomb (1.0 C) of negative charge = 6.25 x electrons Ebonite rod – 1 millionth of a coulomb Carpet zap – billionth of a coulomb 1 coulomb of charge -100 W light bulb in 1 s 10 to 200 C of charge – lightning bolt } Don’t need to copy

Electric Current Electric current is given the symbol “I” and is measured as “the # of coulombs that travel past a certain point in a circuit per second” I = # of Coulombs/second I = q/t I = current (A) q = charge (C) t = time (s) Current is measured with an ammeter (connected in a series)

Sample Problems Lets try these on the board, record the steps on your handout. 1. How many coulombs (or how much charge) pass through a 0.8 A, 100 W bulb in 15 minutes? I = 0.8 A t = 15 min x 60 s/min = 900 s Find q q = It q = (0.8 A)(900 s) q = 720 C Therefore, 720 C of charge pass through a 100W bulb in 15 min. Required: Given: Analysis: Solve: Sentence:

Sample Problems Lets try these on the board, record the steps on your handout. 2. If 1584 C of charge pass through a toaster in 3 minutes, what is the current through the toaster? q = 1584 C t = 3 min x 60 s/min = 180 s Find I I = q/t I = 1584 C/ 180 s I = 8.8 A Therefore, the current through the toaster is 8.8 Amperes Required: Given: Analysis: Solve: Sentence:

Sample Problems Lets try these on the board, record the steps on your handout. 3. How many coulombs of charge pass through a 11.7 A microwave oven in 2 minutes? I = 11.7 A t = 2 min x 60 s/min = 120 s Find q q = It q = (11.7 A)(120 s) q = 1407 C Therefore, 1407 C of charge pass through the microwave oven in 2 minutes Required: Given: Analysis: Solve: Sentence:

Electric Potential Energy = ability to do work Unit: Joule (J) Electrons move through a circuit, pick up energy at power source, and give some up at each load Total energy picked up = total lost during trip around circuit ELECTRIC POTENTIAL = amount of energy carried per coulomb (q) Volts = Joules/coulomb V = J/C

Potential Difference (aka: Voltage) Energy gained or lost by each Coulomb of electrons is the potential difference What we are really measuring is the change in electric potential of electrons from one point in the circuit to another Unit is Volt (V) V = E/q V= potential difference (V) E = energy (J) q = charge (C)

Resistance It is easier to run through air than through water. Why? It's also easier to slide a chair over a smooth kitchen floor than over a thick carpet. Why? Electrons meet with more resistance when they go through some materials than others Lose some of their electrical energy as heat energy. Good conductors have very low resistance Eg) Heating element

Resistance Resistance of something depends on: The material The length of object The diameter The temperature R = V/I Ratio: potential difference across a load : the current going through the load

Electric Circuits A circuit diagram is a simple way to represent a circuit Standard symbols are used, so no labels required Eg: A flashlight circuit: On or off? Copy symbols on p. 457 into your notes. Omit AC