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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 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