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Electricity section 5: 5.1 Introduction - what you need to know about a SERIES CIRCUIT

Doc Brown's Physics exam study revision notes: There are various sections to work through, after 1 they can be read and studied in any order.

INDEX for notes comparing the structure & function of series & parallel circuits


5.1 Introduction - what you need to know about a SERIES CIRCUIT

  • Know and understand that for components connected in series:

    • the total resistance is the sum of the resistances of each component,

    • the same value of current passes through each component in a series circuit - identical current at any point in a series circuit,

    • the total potential difference of the supply is shared between the components - so each component has a different p.d. unless two resistors are identical, so they would have the same p.d. across them.

    • Reminder:

    • Two lamps wired in series, the two cells and ammeter are also wired in series.

  • Know and understand that the potential difference provided by cells connected in series is the sum of the potential differences of each cell (cells should be connected + - + - etc., so non cancel each other out).

AND

Watch out for different styles of circuit diagrams - follow the wires and follow the logic!

e.g. look at the two styles on the circuit 34 and 35 diagrams, the first two circuits I'm analysing on this page!

NOTE: Everything you need to know about series and parallel is included in the first two examples.

There are some questions on series and parallel circuits at the end.

A simple series circuit (compare with the parallel circuit 35 in Part 5.4)

In a series circuit all the different components are connected 'end to end' between the terminals of the power supply e.g. the +ve and -ve terminals of a dc supply (as in the circuit diagram 34 below).

In a series circuit, if you break the circuit at any point i.e. disconnect a component, everything stops working - no complete circuit, therefore no current flow.

You can include a variable resistor in the circuit to vary the p.d. and current to make a wide range of readings to verify the pattern of resistance - which should stay constant if they don't heat up according to Ohm's Law.

BUT, you can investigate the relative ratio of the potential differences across the two resistors.

diagram of circuit to investigation resistors wired in series

SERIES circuit, two resistors wired together one after the other.

R1 and R2 are resistors (e.g. any device/resistance) wired consecutively end to end, this is what wiring in series means. I'm assuming the circuit is powered by a 12.0 V d.c. supply from batteries or power pack.

Reminder: If any part of a series circuit is disconnected, then the whole circuit fails - no current can flow

Three ammeters, A1, A2 and A3 are wired in series with everything else - giving 3 readings I1, I2 and I3 A (amps).

Ammeters are always wired in series with any component whose current is being measured.

Voltmeters V1 and V2 are wired in parallel to measure the potential difference (p.d.) across each resistor - component.

Reminder: Wiring in parallel means each component is independently connected to the positive and negative terminals of the power supply - on separate loops ...

... AND this is how you must always wire a voltmeter in a circuit.

... noting (i) that a voltmeter has a VERY high resistance, so virtually no current flows through it, and so the voltmeter will not affect the ammeter readings,

and (ii) an ammeter is always wired in series in any part of a circuit (series or parallel circuits), and has a very LOW resistance, so there is virtually no potential difference across it and so the ammeter will not affect the voltmeter or ammeter readings.

 

INDEX-notes comparing structure & function of series & parallel circuits


Keywords, phrases and learning objectives for a series circuit

Know how to draw a wiring diagram of a series circuit - how the components are wired one after the other, with no component in a separate loop - apart from the voltmeter wired in parallel across a resistor.


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INDEX-notes comparing structure & function of series & parallel circuits

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