© Boardworks Ltd 2003 Series and Parallel– Simple Circuits

© Boardworks Ltd 2003

Series and Parallel– Simple Circuits


Series vs. Parallel circuits

• What happens when a light goes out in a string of christmas light?

• What happens when a light bulb goes out in your house?


Look at the two circuits shown

In which circuit are the bulbs the brightest?In circuit A the bulbs are the brightest.What happens if you unscrew one bulb in Circuit A?The other bulb stays lit.What happens if you unscrew a bulb in circuit B?The other bulb goes out.What do we call circuit A?Parallel CircuitWhat do we call circuit B?Series Circuit

BRIGHTER

DIMMER

A.

B.


Series Circuits

• When electrons have only one path to follow (like a single slide at a water park)

• If a person stops the current stops, if they close the slide (open a switch) the current will no longer flow.

• A circuit with only one path to follow is called a Series Circuit.


Voltage in a Series• A battery loses all the voltage

it pushes around the circuit by sharing it around all the loads in the circuit.

• Think about when you walk up 12 steps of ladder to a slide. You lose all 12 steps as you go down the slide, then you get the push of the stairs back up to the top.

• In a series circuit, the sum of the voltages lost on the loads equals the total voltage supplied by the battery.


Measuring voltage in a Series Circuit

V2 V3

V1

Set up the apparatus as shown……

…then record the voltages at the locations shown.What do you notice about the readings?For a series circuit, the sum of the voltages for each component is equal to the voltage across the cell or battery.

V1 = V2 + V3

Note: Voltmeters are connected in parallel

Voltmeter Voltage(V)

V1

V2

V3

1.50.750.75


Current in a Series Circuit

Set up the circuit shown below……

…and then record the current using an ammeter in the places shown below.

What do you notice about the readings?The current is the same for each ammeter.In a series circuit the current is the same wherever you measure it.

When measuring current ammeters are always placed in series.

A

AA


Current in a Series Circuit

• Current is shared along each part of a circuit evenly.

• Ex. like water flowing through a hose. No matter what part of the hose you look at, the current that will be flowing will be the same.


Resistors in Series

• When you slide down a water slide if all of a sudden there was no water and you slide down dry plastic you would slow down (probably hurt a bit too…)

• This is just like resistance, as people must slow down riding the slide when they hit the dry bit, there will be less people riding the slide per minute. Think of resistors like the dry part, slowing down electrons in a circuit, decreasing the current (amount of electrons flowing past a certain part of the wire per second).


Resistors in Series

• When resistors are placed in series in a circuit, the total resistance increases and the total current throughout the circuit decreases.


Parallel Circuits

• A closed circuit where there is more than one path for electrons to flow through is called a parallel circuit

• There are three possible paths, electrons can flow to bulb 1, 2 or 3.

• If one bulb goes out, the other ones will not be affected.

• Think about a waterslide park with one slide closed. The kids can still get to the bottom by taking another slide.

• The part of a circuit where it braches off is called a junction point


Measuring voltage II

V1

V2

V3

Voltmeter Voltage(V)

V1

V2

V3

1.51.51.5

Set up the apparatus as shown….

..measure the voltage at the locations shown.

What do you notice about your readings?

For a parallel circuit, the voltage across the

cell/battery is the same as the voltage across

each branch.

V1 = V2 = V3


Measuring current II

Set up the circuit shown below……

…then record the current at the locations shown.What do you notice about the readings?For a parallel circuit, the current that leaves the cell or battery is the same as the current that returns to the cell or battery. The current does not get used up by a circuit, just the energy the electrons are carrying. Pathways with less resistance will have more current flowing through.

A1 = A4

The sum of the currents at a junction point of a parallel circuit is the equal to the current that leaves the junction point or battery.

A1 = A2 + A3 =A4

Ammeter Current(A)

A1

A2

A3

A4

0.8

0.8

0.50.3

A1

A2

A3

A4


• The total current entering a junction point must

Equal the sum of the current leaving the junction point. Loads of different resistance will have different currents.


Resistors in Parallel

• When resistors are placed in parallel you create another pathway so the overall resistance is decreased.

• When the total resistance decrease what happens to the current in the circuit?– Think about I = V/R– It increases!!!!


Resistors in Parallel

• If you only have one pathway, the resistance will be higher than if you have two pathways.

• Therefore, the more resistors you add in parallel, the less total resistance there is and the more current will flow.


The Power of Electricity Power = rate of change in energy or the rate at

which work is done or being transformed.• The unit of energy is the Joule (J). One joule

(J) of energy transformed in one second (s) is called a watt (W) of power.

• 1 Watt = 1 J/s


Calculating Electrical Power

• Electrical power is the rate of change in electrical energy.

• What changes electrical energy to other forms? – Load (light bulb, stereo)

• Calculating Electrical power of a device by using: P(power) = V x I


Energy Consumption

• Power is the amount of energy used over time.

• P = E/t• Power = Energy/time

Switch around equation• Energy = P x t • Create another Triangle• This power rating is usually seen

on electrical devices such as blenders, hair dryers, computer power supplies, and heaters.

E (J) = P(W) × t(s) Energy (Joules) = Power (Watt) × time (seconds)


Large Units of Energy

• A joule is a very small measure of energy.

• 1.0 joule = 1.0 watt X 1.0 second

• Large quantities of energy are measured in kilowatt–hours (kW•h)

1000 W = 1 kW 3600 s = 1 h 1.0 kW•h = 1.0 kW × 1.0 h1.0 kW•h = 1000 W × 3600 s 1.0 kW•h = 3,600,000 J = 3600

kJ


Cost of Electricity

• BC Hydro monitors the electricity used in your home by a meter that measures the energy used in kilowatt-hours

For example, if you used 1500 kW h and BC Hydro costs $0.07 a kw h, how much is your electric bill?


Power Surges

• Why do we have power bars that we connect our computers to?

• Surges can be caused by lightning, turning off large electrical appliances and power company “errors”

• Surge protectors absorb some of the extra electricity and send the rest to ground

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© Boardworks Ltd 2003 Series and Parallel– Simple Circuits