Series and Parallel Simple Circuits Boardworks Ltd 2003

Series and Parallel– Simple Circuits © Boardworks Ltd 2003

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? © Boardworks Ltd 2003

Look at the two circuits shown A. BRIGHTER B. DIMMER What do happens The Series we Parallel In circuit call other ifare Circuit circuit you Circuit circuit Athe bulb the unscrew B? A? stays goes bulbsthe out. lit. a are one bulb the bulb inbrightest. circuit in Circuit B? A? In which circuit bulbs brightest? © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

Measuring voltage in a Series Circuit For a series circuit, the sum of the voltages for each component is equal todo theyou voltage across the orlocations battery. shown. Set up the apparatus as shown…… …then What record notice the voltages about the atcell the readings? V 1 = V 2 + V 3 V 1 Note: Voltmeters are connected in parallel V 2 Voltmeter Voltage (V) V 1 V 2 V 3 1. 5 0. 75 V 3 © Boardworks Ltd 2003

Current in a Series Circuit In a series circuit the current is the same Set up theyou circuit shown below…… …and The What current then do record isnotice the same about current for the each using readings? ammeter. an ammeter wherever you measure it. in the places shown below. When measuring current ammeters are always placed in series. A A A © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

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). © Boardworks Ltd 2003

Resistors in Series • When resistors are placed in series in a circuit, the total resistance increases and the total current throughout the circuit decreases. © Boardworks Ltd 2003

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 © Boardworks Ltd 2003

Measuring voltage II V 1 For parallel circuit, theat. . measure voltage Setado up thethe apparatus What you notice about voltage across the locations shown. as shown…. your readings? cell/battery is the same as the voltage across each branch. V 1 = V 2 = V 3 V 2 V 3 Voltmeter Voltage (V) V 1 V 2 V 3 1. 5 © Boardworks Ltd 2003

Measuring current II For a parallel circuit, the current that leaves the cell or battery is the same as the that returns toat the cellreadings? or battery. The current does not get …then What record you the notice current about the locations shown. Setcurrent updo the circuit shown below…… used up by a circuit, just the energy the electrons are carrying. Pathways with less resistance will have more current flowing through. A 1 = A 4 A 1 Ammeter Current (A) A 1 A 2 A 3 A 4 0. 8 0. 5 0. 3 A 4 A 2 A 3 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. A 1 = A 2 + A 3 =A 4 0. 8 © Boardworks Ltd 2003

• 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. © Boardworks Ltd 2003

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!!!! © Boardworks Ltd 2003

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. © Boardworks Ltd 2003

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 © Boardworks Ltd 2003

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 © Boardworks Ltd 2003

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) © Boardworks Ltd 2003

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 (k. W • h) 1000 W = 1 k. W 3600 s = 1 h 1. 0 k. W • h = 1. 0 k. W × 1. 0 h 1. 0 k. W • h = 1000 W × 3600 s 1. 0 k. W • h = 3, 600, 000 J = 3600 k. J © Boardworks Ltd 2003

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 k. W h and BC Hydro costs $0. 07 a kw h, how much is your electric bill? © Boardworks Ltd 2003

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 © Boardworks Ltd 2003