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# Electric circuits - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about ' Electric circuits' - liuz

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Presentation Transcript

### 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

• 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

• 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

• 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)

• 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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• 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)

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.

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

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

• 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)

• 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 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