Electric circuits2.2

Electric CircuitsRecall: Terminal = electrode = +ve and –ve

endsMetal 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 breakElectrons can’t flow

Electric Circuits There are 4 essential components of a

circuit:1. Source of electrical energy

a. Generator – converts mechanical energy (motion) to electrical energy

b. Cell – converts chemical energy to electrical energy

c. Battery – 2 or more connected cells

2. Conducting wiresa. Metal wires connect all parts of the circuit

Electric Circuits3. Load/Resistor:

Provides resistance to electron flow A device that transforms electrical energy to

another type of energya. Light bulb (lamp)b. Motor

4. Switch - a control device that completes or breaks the circuit

a. Fuse or circuit breaker

Electric CurrentRiver 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 secondElectrons are too numerous to count, so they

are grouped into coulombs (C)

Electric CurrentAmount of electrons or “charges” = coulombs

given the symbol “q”

1 coulomb (1.0 C) of negative charge = 6.25 x 1018 electronsEbonite rod – 1 millionth of a coulombCarpet zap – billionth of a coulomb1 coulomb of charge -100 W light bulb in 1 s10 to 200 C of charge – lightning bolt

}Don’t need to copy

Electric CurrentElectric 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)

Sample ProblemsLets try these on the board, record the steps on your

handout.1. 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.

Required:

Given:

Analysis:Solve:

Sentence:

Sample ProblemsLets try these on the board, record the steps on your

handout.2. 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

Required:

Given:

Analysis:Solve:

Sentence:

Sample ProblemsLets try these on the board, record the steps on your

handout.3. 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

Required:

Given:

Analysis:

Solve:

Sentence:

Electric PotentialEnergy = ability to do work

Unit: Joule (J)

Electrons move through a circuit, pick up energy at power source, and give some up at each loadTotal 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 differenceWhat 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/qV= potential difference (V)E = energy (J)q = charge (C)

ResistanceIt 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 othersLose some of their electrical energy as heat

energy. Good conductors have very low resistanceEg) Heating element

ResistanceResistance of something depends on:

The materialThe length of objectThe diameterThe temperature

R = V/IRatio:potential difference across a load : the current going through

the load

Electric CircuitsA circuit diagram is a simple way to

represent a circuitStandard symbols are used, so no labels

requiredEg: A flashlight circuit:

On or off?Copy symbols on p. 457 into your notes. Omit

AC