Additional Physics – Forces L/O :- To understand how current and voltage behave in a parallel circuit Parallel Circuits Exam Date -

L/O :- To understand how current and voltage behave in a parallel circuit Parallel Circuits Quick quiz: (in back of books) 1)What unit is current measured in? 2)Does an ammeter need to be connected in series or in parallel to a component? 3)Does a voltmeter need to be connected in series or in parallel to a component? 4)Is current the same all the way around a series circuit or does it get shared between all the components? 5)Is voltage the same all the way around a series circuit or does it get shared between all the components?

V 1 A2 Information to write down 1.V1 (voltage down last branch ) = 2.V2 (voltage down first branch ) = 3.V3 (voltage provided by cell) = 4.A1 (current down last branch) = 5.A2 (current down last branch) = 6.A1 (current down last branch) = 1 2 A 1 A3 V 2 V 3 Instructions: Ignore the ammeters and voltmeters, and set up this simple parallel circuit. Then position the ammeter and voltmeter at position 1. Record your results. Then move the voltmeter and ammeter to the next position.

TASK - Collect evidence to support your predictions a)Current remains the same b)Current is shared c)Voltage is shared between the components d)The voltage from the battery is the same all over Assessment - You will be assessed on the evidence you provide for your answer. You should create a table and use the data to back up which statements you think are true Below are the same statements as you had last lesson. Make a prediction to answer these for a PARALLEL circuit

Your evidence... Is your evidence repeatable? How do you know? Is your evidence reproducible? How do you know Is your data accurate? How do you know? Is your data precise? How do you know? Accurate Close to the true value Precise Close to the MEAN value

So the rules: For parallel circuits Current is shared down branches of a parallel circuit Voltage is the same down branches of a parallel circuit.

Evaluating models in science We can use models to explain and understand complicated ideas. While models simplify things, we need to be able to evaluate models to say how they are good or bad.

How can we imagine current? The room is a circuit. All pupils are electrons (they carry energy tokens) A bulb collects an energy token from each electron A cell hands out energy tokens to the electrons An ammeter counts the total number of electrons that have gone past A voltmeter has to count the difference between the amount of energy arriving and leaving a component. We will run two circuits; a series circuit and a parallel circuit.

So in a series circuit: All the electrons provided by the cell MUST go past all the bulbs. (so current is the same all the way round) However – the voltage must get split between each component because some of it must get ‘used up’ as you go past each component.

So in a parallel circuit: Half the electrons go down the first branch and half go down the second branch. (So current is SPLIT down each branch) However – the voltage is the same down each branch, as each electron is arriving with its full amount of energy from the cell.

Some other information: In series; the voltage provided each cell adds up; (so two 3V cells will make a 6 Volt battery) In series; the resistance of the components add up; (so two 4 Ohm resistors adds up make an 8 Ohm total resistance) In parallel; the current will split according to the resistance down each branch. (if both branches have equal resistance the current will split 50:50, however if one branch has resistance of 2 Ohms and the other has a resistance of 1 Ohm, twice as much current will flow down the branch with the lower (half as much)resistance)

Pupil demo Tokens = energy (work done) Pupils = electrons. Room = circuit Pupil hands out tokens = cell 1 Pupil collects token = bulb 1 Pupil counts number of electrons that go past in a given time = ammeter 1 Pupil counts the difference between the number of tokens going into and leaving the bulb = voltmeter 1 pupil needs to add up the total amount of energy given to the bulb in the time limit. (work done)

Proving the equation: We will run the circuit a few times, using different Voltages to see if the rule works. Try the circuit for voltages of 1, 2 and 3 V (this means handing out 1, 2 or 3 tokens at a time)

Does our model actually work? Voltage (potential difference) Work done (total number of tokens collected at bulb) Total charges ( number of pupils past the ammeter) Work done divided by charge Copy this table out, for the last column use the equation of Potential Difference = Work done ÷ Charge If our model has worked the last column should be the same as the first.

1. (a)Complete the sentence below to name the instrument used to measure electrical current. The instrument used to measure electrical current is called (1) (b) In the diagram below each box contains an electrical component or a circuit symbol. Draw straight lines to link each electrical component to its circuit symbol. The first one has been done for you. (Total 5 marks)

2.A student investigates how the current flowing through a filament lamp changes with the voltage across it. She is given a filament lamp and connecting wires. She decides to use a 15V power supply, a variable resistor, an ammeter, a voltmeter and a switch. (a)Complete the circuit diagram to show how she should set up the circuit.

VOLTAGE (V) CURRENT (A) (b)The student obtains the following results. (i)Plot a graph of current against voltage. (3) (ii)Use your graph to find the current when the voltage is 10V. Current A (1) (iii)Use your answer to (ii) to calculate the resistance of the lamp when the voltage is 10V Resistance W (2) (c)(i)What happens to the resistance of the lamp as the current through it increases? (ii)Explain your answer (2) (Total 12 marks)

3.A small torch uses a single cell to make the bulb light up. (a) Label the symbol for a cell and the symbol for a bulb (lamp) (b) The graphs show the voltage across two different types of cell as they transfer the last bit of their stored energy through the torch bulb. Describe the differences that the graphs show between the two types of cell (3) (c)The diagram shows how bright the torch bulb is for different voltages.

(c)The diagram shows how bright the torch bulb is for different voltages. From the point when the voltage of each cell starts to fall, how long will the bulb stay lit: (i) with the ordinary cell? (ii) with the nicad cell?

What have you learnt? Do you know the rules for current in a parallel series Do you know the rules for voltage in a parallel circuit? Can you explain why this happens Can you explain the difference between repeatability and reproducibility? Can you explain the difference between accurate and precise data