2The CELLThe cell stores chemical energy and transfers it to electrical energy when a circuit is connected.When two or more cells are connected together we call this a Battery.The cells chemical energy is used up pushing a current round a circuit.
3What is an electric current? An electric current is a flow of microscopic particles called electrons flowing through wires and components.-+
4simple circuitsHere is a simple electric circuit. It has a cell, a lamp and a switch.wirescelllampswitchTo make the circuit, these components are connected together with metal connecting wires.
5simple circuitsWhen the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around.If there were any breaks in the circuit, the current could not flow.
6circuit diagramScientists usually draw electric circuits using symbols;celllampswitchwires
7circuit diagramsIn circuit diagrams components are represented by the following symbols;cellbatteryswitchlampbuzzerammetervoltmetermotorresistorvariable resistor
8types of circuit There are two types of electrical circuits; SERIES CIRCUITSPARALLEL CIRCUITS
9SERIES CIRCUITSThe components are connected end-to-end, one after the other.They make a simple loop for the current to flow round.If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
10Light Bulbs in SeriesLights connected in a row, one after the other are IN SERIESREMOVE one bulb and the circuit is BROKENIf Circuit is BROKEN, they all go out.
11PARALLEL CIRCUITS The components are connected side by side. The current has a choice of routes.If one bulb ‘blows’ there will still be a complete circuit to the other bulb so it stays alight.
12measuring currentElectric current is measured in amps (A) using an ammeter connected in series in the circuit.A
13Light Bulbs in Parallel Lights connected on different wires that share the same current flow as the original wire provide multiple paths for electricity to flow.REMOVE one bulb and the circuit is STILL ACTIVE IN OTHER AREAS.Other remaining bulbs still have current and glow
14measuring current A A This is how we draw an ammeter in a circuit. PARALLEL CIRCUITSERIES CIRCUIT
15measuring current SERIES CIRCUIT current is the same at all points in thecircuit.2A2APARALLEL CIRCUIT2A2Acurrent is sharedbetween thecomponents1A1A
16copy the following circuits and fill in the missing ammeter readings. ?3A3A4A?1A??4A4A1A?1A
17measuring voltageThe ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeterV
18measuring voltageDifferent cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current.Unlike an ammeter a voltmeter is connected across the componentsScientist usually use the term Potential Difference (pd) when they talk about voltage.
19measuring voltage V V This is how we draw a voltmeter in a circuit. SERIES CIRCUITPARALLEL CIRCUIT
20series circuitvoltage is shared between the components3V1.5V1.5V
21parallel circuit voltage is the same in all parts of the circuit. 3V
22measuring current & voltage copy the following circuits on the next two slides.complete the missing current and voltage readings.remember the rules for current and voltage in series and parallel circuits.
26SERIES CIRCUITS - RESISTANCE Resistance means to “resist” or slow down the flow of current. RESISTORS are devices, like light bulbs, that make use of this slowing down of current.
27Total Resistance in Series Resistance is measured with an Ohmmeter, named after the unit of Resistance, the Ohm .In a series circuit, you ADD all the resistance in that wire section together.3 3 + 3 = 6 total
28PARALLEL CIRCUITS - RESISTANCE Resistance along a parallel circuit is reduced because you give the current another way to go, multiple paths!!BUT THINGS GET WEEEEEIRD when you add these up...
29Total Resistance in Parallel (1/R1 + 1/R2) = 1/RtotalIn a parallel circuit, you ADD the INVERSE of all the resistance in that wire section together and then take the inverse of the answer…You are making the pathway BIGGER for the current to flow through by putting resistors side by side – parallel.3 3 1/3 + 1/3 = 2/3 now flip and divide1/Rtotal = 2/3 (then press 1/x button) = 1.5
30ResultsWhen you added these two together inversely, the total resistance was LOWER than either of the resistors.That is because you are providing more area for the charge to flow, so you are reducing resistance.3 3 1.5 Total
31WHICH IS BRIGHTER?So… you know that resistance is different in these circuits. Which type of circuit would allow current to flow faster, making the brightest bulbs?SERIES CIRCUITSPARALLEL CIRCUITS?
32WHICH IS BRIGHTER?The bulbs in PARALLEL will be brighter because the circuit allows current to flow more easilySERIES CIRCUITSPARALLEL CIRCUITS
33Combination CircuitsCombo circuits contain both parallel and series portions in one single circuit.
34Solving Combo Circuits – STEP 1 Solve for the Current going through the total circuit.STEP 1Calculate total resistance of Parallel path first.(1/3 + 1/9) = 1/0.44= 2.25
35Solving Combo Circuits – STEP 2 Solve for the Current going through the total circuit.STEP 2Now it is as if the circuit is just a bunch of resistors in series, EASY!Add the resistance together to get the total:= 2.25
36Solving Combo Circuits – STEP 3 Solve for the Current going through the total circuit.STEP 3Total R = I = V / R = 120/20.25I = 6 A2.25
37Solving Combo Circuits CHALLENGE Solve for the Current going over the 3 resistor ONLY
38Solving Combo Circuits – STEP 1 Solve for the Current going over the 3 resistorSTEP 1Remember that current along a series circuit is always the same at all points.Current in a parallel circuit is shared according to I = V / R6A?
39Solving Combo Circuits – STEP 2 Solve for the Current going over the 3 resistorSTEP 2Must find the voltage going across the parallel path!!!Voltage at parallel branch = the total I X total R of the branchTotal I = 6 ATotal R = 2.25 V = 13.5 V6A13.5 V?
40Solving Combo Circuits – STEP 3 Solve for the Current going over the 3 resistorSTEP 3V = 13.5 VNow just calculate current at 3 resistorI = V / R = 13.5 / 3 = 4.5 AAnd at the 9 resistorI = V / R = 13.5 / 9 = 1.5 A6A13.5 V4.5 A1.5 A
41Power in CircuitsRemember that power is just a measure of how fast you do work.In circuits Power is the same. Work is voltage and the rate is CurrentUnit of Power is a WattP = VI
42Calculate Current with Power A 40 Watt light bulb is connected to a standard 120 V outlet.What is the current being drawn through the bulb?P = VI… I = P / V = 40 / 120 = 0.33 AA brighter 100 W bulb?0.83 AMore current = More power usually