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Electric circuits

Electric circuits. 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.

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Electric circuits

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  1. Electric circuits 2.2

  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

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

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

  5. Electric Current • River current = the volume water that flows past a certain point in a specific time (m3/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)

  6. Electric Current • Amount of electrons or “charges” = coulombs • given the symbol “q” • 1 coulomb (1.0 C) of negative charge = 6.25 x 1018 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

  7. 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)

  8. Sample Problems Lets try these on the board, record the steps on your handout. • 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.

  9. Sample Problems Lets try these on the board, record the steps on your handout. • 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

  10. Sample Problems Lets try these on the board, record the steps on your handout. • 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

  11. 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

  12. 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)

  13. 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

  14. 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

  15. 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

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