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# An investigation into what affects the resistance of wire

Extracts from this document...

Introduction

An investigation into what affects the resistance of wire

Aim:

Aim of this investigation is to find out what affects the resistance of a wire, e.g. length of the wire, area of the cross section and temperature. But we are specially looking at the length of the wire. How the length of the wire affects the resistance if a wire?

Prediction:

I predict that if the length of the wire increases then the resistance will increase too in proportion to the length

Hypothesis:

My hypothesis is if I increase the length of the wire, the resistance will be greater because as the length of the wire increase there will be more space and more collision and if there is shorter space, there will be less collision as is fewer spaces there will be few free electrons whereas in a larger area there will be more free moving electrons, this will increase the number of successful collision. The current flowing through the wire is proportional to the potential difference across it, providing the temperature stays the same. I expect my out come of my result’s graph would look like this. As I have said before, resistance of the wire increases in proportion to increase in length. I am going to carry out an investigation to find out does the length really affects the resistance. I will be checking the resistance of the wire with different length.

Resistance

(Ω)

Length of wire (cm)

Scientific background:

• Current is the flow of electrons round the circuit.
• Voltage is the driving force that pushes the current round.
• Resistance is anything in the circuit which slows the flow of current down.

There would be a balance in a circuit. The voltage is trying to push the current around the circuit and the resistance is against it, the relative sizes of the voltage and resistance decide how big the current will be. If you increase the voltage, then more current will flow. If you increase the resistance, then less current will flow.

People normally believe that current flow from positive to negative. However after electrons were discovered it is now decided that current flow from negative to positive as electros are positively charged. So they will be repelled from negative side and will be pulled to the positive side.

I will be connecting my components in series except the voltmeter which I will have to connect in parallel to 100cm long 24 standard wire gauze. This is the wire I will be investigating the resistance. All the components will be connected in a line, end to end. It is in a series, so if one component get disconnected, the circuit is broken and other component will stop working. In series circuit:

• The total resistance is sum of all the resistance in the circuit.
• The same current flows through the all part of the circuit.
• The potential difference of the powers supply is shared up between the components, so the voltage will be added up to equal the powers supply.
• If the resistance of a component is bigger, the share of potential difference will be bigger too.

Voltmeters are always connected in parallel to any components in the series and ammeters are always place in the series anywhere in the circuit. The reading will be the same wherever you place in it the circuit.

Ohm’s law: The current flowing through the wire is proportional to the potential difference across it. It means, if I double the potential difference, the current is doubled too.

 Quantity Symbol Standard Units Formula Potential difference V Volts, V V = IR Current I Amperes, A I = V/R Resistance R Ohms, Ω R = V/I

Resistors can be used to reduce the current in a circuit and slow down the force of the current. A variable resistor is used to vary the current in the circuit. You can choose the resistance in a variable resistor, weather you high resistance or lower resistance. As the sliding contact moves, it varies the length of wire in the circuit. Some of the factors which affect the resistance:

• Wire width: If the wire width is increased, the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there will be fewer collisions.
• Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms, as the atoms moves into the path of the electrons. This increase in collisions means that there will be an increase in resistance.
• Material: The type of material of the wire will affect the amount of free electrons, which flow through that wire. This is because the number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high numbers of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.
• Length of wire: if the wire length increased, the resistance will increase. This is because of the increase in the space for free electron to collide. Due to this more amount of free electron will make successful collisions. Greater collision means more energy transfer which leads to higher resistance.

Apparatus:

• Voltmeter: This was used to measure the voltage across the constantan wire. This shows us the voltage of the wire in volts

• Ammeter: This was used to measure the current flowing through the components. This showed how much current was flowing through each component in amperes or amps.
• Powers supply: This was used to power the circuit. We had to use the crocodile clips to connect the wires.
• Meter ruler: It is 100cm long ruler which was used to measure the length of the wire. Wire was connected on the ruler with the help of crocodile clip and bit of sellotape.

• Crocodile clip: This was used to hold the wire to the ruler so that we can measure and place connect the crocodile clip where we need. Also at the end of wires to hold them together.

• Constantan wire: This is 24SWG wire, a bit longer that 100cm. This was used to carry the current, to test the resistance in order to do the experiment.We used constantan wire because its resistance does not vary with temperature.

• Sellotape: This was used to held the wire in possition. This made it easy for us to do the experiment smoothly and quickly.

Middle

Through out this whole experiment, I am keeping some of the factor same during the experiment:
• The temperature: I am keeping this fair because according to the scientific background, if the wire get hot by the surrounding or any others thing, there will be more collision with the free moving electron in the wire and there will be a slight increase in the resistance.
• Thickness of the wire: If I change the thickness of the wire, I will get different result each time. According to the scientific background if the wire is wide there will be more space, which means fewer collision, however if the wire is narrower, there will be less space which mean more collision. So each time if I change the wide, there will be different resistance each time.
• The amount of current flowing in the circuit: We are trying to find out the resistance of the wire in different the measurements. We have to keep the power in D.C same. So that we can find out the resistance in different measurements. If we change the current, then we will different result with different measurements of wire.
• Repeat the experiment 3 times: If we repeat the experiment three time. Then we get more accurate and fair results. So you can compare the results with the others results to make sure is everything is fine and accurate. Also we then are able to find the average of the repeats which then make sure our results are reliable.

Safety:

• Do not carry out the experiment near or in wet areas because water is a very good conductor of electricity, so this could be very dangerous.
• Do not touch the wire when the powers supply is switched on because the current would heat up the wire and it will burn the fingers.
• Never leave the powers supply on for a long time because will heat up the wire and it will burn.

Variable and Factors:

• Length of the wire is variable as I will be changing several times throughout the experiment because to find out the resistance affected by the length, I will be testing the resistance in many different lengths. I will have 10 different kind of length and I will be repeating the same length 3 times to get accurate results.
• Resistance is variable because I will be repeating the experiment three times with different resistance. 1st time lower resistance, 2nd time medium resistance and 3rd and final time higher resistance. I will be using a variable resistor.
• Mistakes we human make are factors because it can affect the experiment if anyone makes any mistakes.

Conclusion

I still thing I did not get 100% accurate correct results because as the cross fade away, it is really hard to tell is it disappeared or not, also the fast of toggling through the buttons in stop watch will vary. But we did try to make sure we got accurate results by just keeping one person for these jobs. I would make sure the wire wasn’t getting hot because of the wire gets hot, then there will be different results as temperature is different. I would make sure that I let the wire cool down before I use it again.

To further my investigation on resistance of the wire I could change the material of the wire, may be copper wire or any other wire to make sure it still support my prediction or I would carry out the experiments in different temperatures, which will take more time. I would have change the number scales into even more accurate.

Overall as my conclusion, I conclude that if we increase or decrease the length of the wire, it will increase or decrease the resistance of the wire in proportion to the length of the wire. The length, temperature, cross section and wide of the wire do affect the resistance of the wire. My results were not 100% accurate because I got two anomalous somehow. However the results supported my hypothesis and my prediction because I referred my prediction according to the scientific background.

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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