# To find out what variable affects the resistance of a wire.

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Introduction

16TH NOVEMBER RESISTANCE INVESTIGATION JAMES LAGDEN PAGE

RESISTANCE INVESTIGATION

AIM: To find out what variable affects the resistance of a wire.

WHAT IS RESISTANCE? : A current is a flow of charge, it is the movement of electrons from the negative to the positive terminal of a cell. For current to flow there must be a complete circuit with no gaps. Current is measured in amperes (amps). 1amp has a flow of 6 million million million electrons per second. We say that a wire has a certain resistance to the current, and the greater the resistance, the greater the current needed, to continue the flow of electrons (current) through the wire. Metal atoms are held together by a "sea of electrons." Each metal gives up one or more of its electrons into the "sea of electrons." The electrons can drift about in the metal and so are mobile electrons. These free electrons explain how electricity can pass through solid metals. Most metals are dense, therefore their atoms must be packed closely together. To calculate resistance the equation below is used:

Resistance (R) = Potential difference across a resistor (V) R = V Current flowing through it, in amps (I) I

P.d. is measured in volts (V) current is measured in amps (A) resistance is measured in ohms (Ω)

According to Ohms law, which states

Middle

(Source= physical processes, Nick England)

Wire type (material) – Different materials will have different numbers of atoms and so the flow of electrons will depend on the type of material and the number of atoms in it.

(Source= physical processes, Nick England)

APPARTUS: Wire: Copper 26, 32 (standard wire gauge.)

Nichrone 26, 32, 36 (S.W.G.)

Constantan 26, 32 (S.W.G.)

The standard

Multimeter /OHMmeter Ω - to measure the resistance of the wire. This is the most accurate resistance meter I can use because if I use an ammeter and a voltmeter than there are two readings to measure and calculate and the resistance will not be as accurate as if an ohmmeter were used. The ohmmeter can measure the resistance to the nearest .1 Ω so it is very accurate.

Metre ruler – This is used to measure the length of wire, it is quite accurate as it can be used to measure to the nearest .5 mm but if the wire is not totally straight

it will not be efficient. The wire will not be straight

as it will have been be coiled, to keep this a fair test

I will try to straighten the wire as much as possible

but not stretch it, as this would change the resistance.

Electrical leads and crocodile clips – I will have to

take into account the resistance of these wires and

clips when I perform my experiment as they could

have a significant difference on my final results. I

Conclusion

The scientific idea that if you double the length of the wire, you double the number of atoms in it, so doubling the number of electron collisions is true in accordance with my experiment. The results support my predictions well and most of the results turned out the way I had expected. I had predicted that when length changed so would the resistance. I also predicted that if length doubled then so would the resistance as is stated in Ohms Law. (See intro. ‘What is resistance?’) This prediction was not quite true, as the resistance did not double when the wire length was doubled i.e.

10cm - 0.73Ω doubled =1.46Ω

20cm - 1.46Ω doubled =2.92Ω 40cm - 2.86Ω doubled =5.72Ω

80cm - 6.13Ω doubled =12.26Ω

Although these lengths appear to double at first, some have higher steps and some have lower steps and so in my experiment Ohms law was not true.

From my results I conclude that when the length of a wire is increased the resistance will increase proportionally but not always, as stated in Ohm’s Law in the same steps. I conclude that the steps will not always be accurate but will be quite near each other, that they will always be within the region of ‘double the length, double the resistance’.

I thus conclude that when a wire is lengthened,

the resistance of that wire increases.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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