In metals, the outside electron is held very weakly by the nucleus, (see fig 1). This is particular to metals only. When a charge is applied to the wire, the atoms will move in the electronic current. When the wire is heated, the metal atoms will move about, making it difficult for the electrons to pas through, therefore increasing the resistance.
Key Factors:
During my experiment, I will keep the cross sectional area of the wire, and the type of metal constant throughout, as a change in these could cause the resistance to change and make the experiment unfair. I plan to control the temperature by keeping the voltage below 6V, and to wait for the wire to cool down after each experiment. Also I must take into account the room temperature and how it will increase as everyone will be carrying out the experiment. I will monitor the temperature by using a thermometer. The wire shall be made from Constantine and shall be kept the same throughout the experiment. I will change the resistance by changing the length of wire used. It will start at 90cm long and decrease 6cm each time. To measure the current I will use an Ammeter connected in series with the circuit, (see circuit diagram). It will measure the current in Amps, flowing through the component. Likewise, to measure the voltage, I will use a voltmeter which will be connected in parallel around the wire component. It will measure the voltage across the component. To find the resistance I will divide the voltage against the current as V=I x R is the equivalent to R = V / I. I need to take into account that while carrying out my experiment; I will need to make sure that the wire component is as straight as possible to ensure accuracy. I plan to measure accurately and measure the sensitivity of meters. I will collect 15 results and repeat the experiment 3 times to ensure reliability.
Equipment List:
- Ammeter
- Voltmeter
- Power Pack
- Wires
- Metal wire (90cms)
- Resistor
- Crocodile Clips
Prediction:
I predict that the longer the wire is the more resistance their will be. I will be interested to find out from my results whether the distance is directly proportional to the length. In , the atomic theory is a theory of the nature of . It states that all matter is composed of . The theory applies to the common , namely , and . I believe that if a wire is longer then there will be more atoms for the electrons to have to pass by, therefore increasing the resistance. A shorter wire will have fewer atoms, and less resistance than a longer one. Also, Ohms Law states that Voltage is proportional to the Current in a circuit and so a graph showing Voltage against Current should give a straight line. This will show that as length increases, so does the resistance, and if you double the length of a wire, you are doubling the resistance also.
Method:
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Set up a circuit like the one shown below. Make sure that the Ammeter and the Voltmeter both work.
- Once this has been set up, measure out the length of the wire. Start at 90cm and decrease 6cm each time.
- With the length of the wire measured, connect it to the circuit with crocodile clips.
- Turn on the power pack making sure the voltage is low, to prevent the wire melting, and to ensure your health and safety.
- Turn on the Ammeter and the Voltmeter and record the current and voltage. From this work out the resistance using Ohm’s Law: Resistance = Voltage / Current.
- Continue decreasing the length of the wire by 6cm. Record the current, voltage, resistance and length.
- Repeat the experiment three times to ensure accuracy in the results.
Trial Runs:
Above (table 1) shows the average results from my trial runs. During my preliminary investigation, I used a wire with thickness of 20 swg. The results and the graph below both support my predication, and show that the longer the length of wire used, the higher the resistance will be. The gradient of the graph shows the resistance increasing in ohms, as the length of the wire increases in cm. The graph suggests that the length is directly proportional to the resistance. However, my results at 30cm and 60cm show clearly that the resistance is not proportional to the length, as double 0.31 Ω is not 0.52 Ω.
While carrying out my preliminary investigation, I have learnt that during experiments, I must keep the voltage low as the wire may melt otherwise. Also I must not let the wire touch the resistor by accident, as this increases the Amp and Voltage reading, and will make the experiment results inaccurate. These factors will help me to plan future experiments and collect better and more accurate results.
From the graph I can obtain the resistance from the gradient. A straight line is y=mx+c, m being the gradient and c being the intercept. Resistance is equal to the inverse of the gradient on a current verses voltage graph, and in Ohms Law R = V/I and on a Voltage by Current graph, the resistance is the gradient.
