Electric circuits
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Electric circuits. 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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Electric circuits

Electric circuits


Electric circuits1

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 circuits2

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


Electric circuits3

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


Electric current

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)


Electric current1

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

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Don’t need to copy


Electric current2

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

      • q/t = Ampere “Amp” (A)

        I = current (A)

        q = charge (C)

        t = time (s)

  • Current is measured with an ammeter (connected in a series)


Electric current3

Electric Current

  • http://www.youtube.com/watch?v=bMDVl6yRLNI&list=PLdIVKwXe8Up9z0pJGe0oLY5-yLbsaz_b7&index=3


Sample problems

Sample Problems

Lets try these together, 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.


Sample problems1

Sample Problems

Lets try these together, 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


Sample problems2

Sample Problems

Lets try these together, 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


Electric potential

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

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)


Potential difference

Potential Difference

  • http://www.youtube.com/watch?v=-ke28lL8C9g&list=PLdIVKwXe8Up9z0pJGe0oLY5-yLbsaz_b7


Resistance

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


Resistance1

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


Resistance2

Resistance

  • http://www.youtube.com/watch?v=9vddcxMATiI&list=PLdIVKwXe8Up9z0pJGe0oLY5-yLbsaz_b7


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