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Electrical resistance

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Carrie Edwards                           Electrical resistance

Electrical resistance is the slowing of a current through an electrical circuit.

The current is a word used to describe the flow of electrons, and is measured in Amps.

 Resistance happens in all electrical circuits.

 Resistant, is a property of any object or substance of resisting or opposing the flow of an electrical current.

  As a conductor conducts electricity as current, a resistor is the opposite. It slows the current down, it is another hurdle for it to pass through.

  Resistance cannot be measured directly but can be calculated from the current flowing along a wire and the voltage difference across it (potential difference)

 Resistance is then calculated using the equation:

  R = V                        Where: V =  Voltage difference across wire (volts)

         I                                       I =  Current flowing along wire  (amps)

                                                 R = Resistance of wire (ohms or     )

One way resistance can occur is through the wire. The factors that affect the resistance of a wire is;

1.Length of the wire

2.Materials of the wire

3.Temperature of the wire

4.Thickness/cross section of the wire

Length can change the amount of resistance. In a stretch of wire, collisions of electrons take place. If the length of the wire was doubled, I predict that the number of collisions would also double, therefore increasing resistance, so

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  I will record my results of the different lengths and thicknesses of the wires and list them in a table.

 Once I have set up my circuit, with all the equipment in the right places I will add the wire and take a reading using the voltmeter and ammeter readings.

 My results shall give me a better understanding of resistance in the wire and I will try to examine closely how to reduce resistance in a circuit with evidence from my results.

 It is important that during my investigation I make it as fair and safe as possible.

 I can therefore take into consideration the following points:

 * I shall make sure that the power pack is turned on safely, when I have put everything else into the circuit, so that there is not a risk of being electricuted.

 * Also I shall make sure that any liquids or substances that are nearby in the Scince lab are kept well away from the power pack.

*  I shall keep the crocadile clips closed whilst not in the circuit as someone could be injured by them.

*  Wrapping wire up when not in use is essential as someone could trip up from it if dropped on the floor or it could get tangled up and cause interruptions whilst carrying out my experiment.

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It is important that this experiment is carried out accurately and precisely to give me the results that I am after.

 Apparatus for Investigation

1 x Power pack

1 x Voltmeter (to measure volts)

1 x Ammeter (to measure ampres-current)

Crocadile clips


Carboard tube (to wrap the wire around)

Variable Resistor


As I have now planned my experiment, I can draw up my method that I will use for my actual experiment:

  • Set up Apparatus
  • Set the power pack on as low a voltage as possible, so that there is not too high a voltage passing through the current.
  • Place the 1m of wire between the 2 crocadile clips to complete the circuit if necessary wrap the wire around the carboard tube.
  •  Turn on the power pack and record the readings on the Ammeter and Voltmeter, remembering to turn off the power pack between the readings.
  • Alter the variable resistor and take a second reading of 1 meter wire.
  • Take 3 readings of current as each of the lengths
  • Record readings in a table
  • Work out the resistance using Ohms law:   R = V


  • Do this for both thicknesses of wire
  • I will make my experiment fair by only changing one variable, in this case, length.
  • I will keep all the other factors constant
  • I will take 3 readings for each length in order to draw an accuartate conclusion at the end  of the experiment.
  • I will keep the voltage low, as it will cause high currents that will heat up the wires.



















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