Book page Syllabus 2.8, 2.9, Series and parallel circuits

Transcription

1 Book page Syllabus 2.8, 2.9, 2.14 Series and parallel circuits

2 Find the Fib! (1) The symbol for a bulb is (2) In a parallel circuit potential difference is the same as the supply voltage on all branches. (3) A voltmeter is used to measure the current through a device

3 (1) The symbol for a resistor is (2) In a series circuit potential across each component adds up to the supply voltage. (3) A voltmeter must be set up in series.

4 (1) A switch must be closed for current to flow. (2) Potential difference is measured using an ammeter. (3) A ammeter must be set up in series.

5 (1) Potential difference is measured in amps. (2) The symbol for a switch is (3) A cell is necessary to push electrons around a complete circuit.

6 Starter Are they parallel or in series?

7 Aim Know how series and parallel circuits are used Know the relationship between current, voltage and resistance Key words Ohm Ohm s Law Resistance - Battery - Cell - resistor

8 Have you ever wondered The bigger picture Where do we need circuits in real life?

9 What are series and parallel circuits? Circuit components can be wired in series or parallel. A series circuit has all its components wired in the same loop. These tree lights are wired in series. A parallel circuit contains junctions and so there is more than one path for the current. Car headlights are wired in parallel. What would happen if they were wired in series?

10 In a series circuit One switch can turn all the components on and off together If one bulb or any other component breaks, it causes a gap in the circuit and all other bulbs will go off The voltage supplied by the cell is shared between all components The more bulbs are added, the dimmer all light bulbs get The larger the resistance of the component, the bigger the share of voltage

11 In a parallel circuit Switches can be placed in different parts of the circuit to switch each bulb on and off individually or all together If one bulb or any other component breaks, only the bulbs on the same branch of the circuit will be affected Each branch of the circuit receives the same voltage, so if more bulbs are added to a circuit in parallel they all stay bright Total voltage = Voltage branch 1 = Voltage branch 2

12 Current in a series circuit In a series circuit the current is the same in all parts Current is not used up as it passes around the circuit Size of current depends on voltage supplied The current will double if another cell is added in series The extra energy allows more charge to flow per second If more bulbs are added, the current gets less, because bulbs have resistance The more bulbs the more resistance in the circuit When the resistance is higher, less current will flow

13 Current in parallel circuits In a parallel circuit the current is split At each branch the current will divide What goes in, must come out

14 Fill in the blanks If you add two more identical cells into a circuit in series, the current in the circuit will treble and the potential difference will. treble This is only true if the cells are connected with the positive and negative terminals in.if the same direction you add two more identical bulbs into a treble circuit in series, the resistance will the current through each bulb will decrease and the potential difference across each bulb will be a third of the potential difference across the cell Stay the same, decrease, halve, double, treble, drop by two thirds, the same direction, different directions, a third of, the same as

15 Fill in the blanks If you add two more identical cells into a circuit in parallel, the current in the circuit will treble and the potential difference will. stay the same This is only true if the cells are connected with the positive and negative terminals in. the same direction If you add two more identical cells into a circuit in parallel, the current through each bulb will drop by two third and the potential difference across each bulb will be the same as the potential difference across the cell Stay the same, halve, double, treble, drop by two thirds, the same direction, different directions, a third of, the same as

16 Resistance All circuit components offer resistance to the flow of charge Connecting wires allow charges to flow easily Wires have a low resistance Some components need a lot of energy to push the charges through. This energy is usually converted to heat These components have a high resistance

17 Definition of Resistance. Resistance is a property of a conductive material that affects how much electrical current can flow through the material. A conductor with a high resistance, is very good at limiting the flow of electrons through a circuit. The units of resistance is the Ohm (Ω). Voltage, current and resistance can be linked by Ohm s law: Voltage V (V) = current I (A) x Resistance R (Ω) V = I R Example When a voltage of 12V is applied across a buzzer a current of 0.1A flows. Calculate the resistance of the buzzer Solution R = V I R = = 120Ω

18 Different size resistors 6.5 A A current A 2 A 3 A 4 1 Ω 2 Ω 1.5 Ω If bulbs with different resistances are connected in parallel to a 3 V battery, what will the current be through each? A 2 A 3 A 4 3 A 1.5 A 2 A The same voltage will cause a larger current to flow through a small resistance than a big one, so the bulb with the lowest resistance will have the biggest current.

19 Plenary: Comparing circuits

20 Multiple-choice quiz

21 Ohm the unit of resistance Key words Ohm s Law - A law relating the voltage difference between two points, the electric current flowing between them, and the resistance of the path of the current. V = IR, Resistance the opposition to the flow of charge Resistor a component that opposes the flow of charge Battery two or more cells joined together Cell A chemical source of voltage