Electrician asked to repair an old radio. He believes that he needs a resistance of 1.9 ohms, which is not easily obtained - investigation to help him resolve the problem

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Physics coursework

An electrician has been asked to repair an old radio. He believes that he needs a resistance of 1.9 ohms, which is not easily obtained.

I have been provided with some reels of resistance wire and I will plan and carry out an investigation to help the electrician solve his problem.

 

I believe there are a certain number of independent variables which may influence the resistance of a wire; 1) The temperature of the wire

                                 2) The diameter of the wire

                                 3) The length of the wire

                                 4) The type of wire

I am choosing to investigate the length of the wire because I believe it affects resistance, as my scientific knowledge tells me;

Current

For current to flow, there must be a complete circuit. Current flows from the positive to the negative terminal of the power supply, but electrons flow in the opposite direction. Current is measured in amps (A) by an ammeter connected in series with a component in the circuit. The current is driven round a circuit by voltage of the power supply or potential difference.

                                     Current= potential difference

                                                           Resistance

Voltage

Potential difference is measured in volts (V) using a voltmeter connected in parallel across a component in a circuit. Voltage can be defined as a measure of how much energy the electrons are carrying around to the things in the circuit. It a series of readings from an ammeter and a voltmeter are taken and plotted, the graph should look like this;

                           Potential difference = current x resistance

Resistance 

                                                                                                         

From the above we can see there is an obvious relationship between resistance, potential difference and current. This is Ohm’s law: the current through a resistor (at constant temperature) is directly proportional to the voltage across it. Therefore:

         

                                       Resistance = potential difference

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                                                                 Current

A long coil of wire has a high resistance, this is because it takes more current to travel down it than a short piece of wire, this is like a runner running a race; it takes more out of a runner running 1000m at the same speed as someone running a race of 10m. There are more atoms in a longer piece of wire and therefore ...

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