Resistant Wire example essay topic

Aims and hypotheses This investigation is designed to look into the resistance of different material in the form of wires and their conducting capability in different shapes. In order to do so, the materials are to be tested for their resistance in the shape of wires, and the hypotheses are such that different thickness and length of the wire and the material that makes up the wire itself will affect the electric conduction capability. Hence, the factors are: The thickness of the wires: 1, 2, 3 and 4 mm in diameter The length of the wires: 25, 50, 75 and 100 cm long The material of the wires: copper, iron, constantan and nichrome There will be 16 tests to be carried out The experiment will require both the readings of voltage and current in order to produce the value of resistance according to the formula: R = V / I (Resistance is measured in Ohms) The power supply, however, is varied between 0-12 V with 1 V interval so that a series of results can be obtained with the single factor altered: a graph of V against I can be drawn and an average resistance can be produced in this case, rendering it a fairer test. Since each test does not take long, the tests can also be repeated to obtain a more accurate mean. DC supply is used so that the voltage and current are not fluctuating while a steady reading is needed to be obtained. To make it a fair test, only one factor should be altered at a time.

When the material of the wire is being tested, the length and the diameter of the wires should be the same at 1 mm wide and 25 cm long. When the length and the diameter are being tested, the wire used should be made of copper, with the diameter and length remaining at 1 mm and 25 cm where possible. Prediction An atom consists of a nucleus and orbiting electrons. These electrons can create a flow of current, so the more free electrons there are, the more conducting capability that material has; thus copper is more conductive that iron. Alloys tend to have less free electrons so they will be less conductive. The order of resistance is consequentially copper, iron, constantan then nichrome increasingly.

Wires with wider diameter have more free electrons because the cross-section surface area is larger in proportion to the length, so the wider the wires are, the less reactive they would be. Resistance is proportional to the cross-section are of the wire given that the length and the material should be the same. Longer wires will cause an increase in resistance because the electrons have to travel past more atoms and collisions between the electrons and the atoms are more likely then in shorter wires. Resistance should also be proportional to the length of the wires. Methods The equipment needed consists of: A variable DC power pack Ordinary wires An ammeter A voltmeter 2 crocodile clips Assorted wires for tests Then a circuit is set up in the same way as the illustrated diagram below.

Connect the wire to the circuit by the crocodile clips Take the voltage and current readings from the meters Increase / decrease the supply from the power pack and take the readings again Repeat the experiment with different pieces of wire Safety precautions Make sure that the circuit is properly connected before turning the power supply on, and do not touch the apparatus, especially the tested, naked wires until the power is switched off The changing of the tested wires should only occur when the power is off Do not carry out the experiment in wet areas, as water is a very good conductor. Do not switch on the power pack when there is no resistant wire and do not turn the power supply up too high because normal laboratory wires may melt Background knowledge Using a circuit such as this one on the left, an important general relationship can be seen. The variable resistor is used to control the current in the circuit and the voltmeter measures how the potential difference (voltage) across the resistor varies. Provided that the temperature does not change significantly, the results give a graph looking like this. This means that the current is proportional to the p. d. The relationship is called Ohm's law.

Ohm's law only applies if the temperature is constant, and does not apply to all electrical components. We can write Ohm's law in symbols: V I Or V = IR And R is the resistance of the resistor. It can be rearranged so that R is the subject, hence: R = V / I The larger the resistance, the greater the gradient will be. Gradient of the graph gives the value of resistance. Ohm's law does not always apply.

A light bulb in place of the resistor in the circuit gives a different pattern for the current and voltage relationship, as shown in the graph. Here the current and voltage are not proportional. The bulb obviously gets hotter and hotter. Since "resistance" is measured by the gradient of the graph, we have here an example where the resistance is increasing. A heat-dependent resistor or thermistor gives the opposite pattern. Its resistance decreases as the temperature rises But obviously we are dealing with "normal" resistors in this investigation, so the gradient of the graphs obtained should be the same throughout - in a linear fashion - and the resistance should remain constant as the voltage / current is altered..