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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:
- 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 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

- 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 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 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)

- q/t = Ampere “Amp” (A)

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

Electric Current

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

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 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 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

- 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)

Potential Difference

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

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

- Ratio:

Resistance

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

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