Resistance Investigation

Aim:

To investigate the factors affecting the resistance of a wire varying the length and the voltage and the type of material used.

Plan:

Equipment:

* Meter ruler

* PSU

* Amp meter

* Voltmeter

* Multi meter (used as Ohmmeter)

* Croc clips

* Wire, 100cm+ of Nichrome

Scientific Knowledge:

The scientific knowledge is based on Ohm's law, which states then relationship that the amount of steady current through a large number of materials is directly proportional to the potential difference, or voltage, across the materials. Thus, if the voltage V (in units of volts) between two ends of a wire made from one of these materials is tripled, the current I (amperes) also triple; and the quotient V/I remains constant. The quotient V/I for a given piece of material is called its resistance, R, measured in units named ohms. The resistance of materials for which Ohm's law is valid does not change over enormous ranges of voltage and current. Ohm's law may be expressed mathematically as V/I = R. That the resistance, or the ratio of voltage to current, for all or part of an electric circuit at a fixed temperature is generally constant had been established by 1827 as a result of the investigations of the German physicist George Simon Ohm.

Alternate statements of Ohm's law are that the current I in a conductor equals the potential difference V across the conductor divided by the resistance of the conductor, or simply I = V/R, and that the potential difference across a conductor equals the product of the current in the conductor and its resistance, V = IR. In a circuit in which the potential difference, or voltage, is constant, the current may be decreased by adding more resistance or increased by removing some resistance. Ohm's law may also be expressed in terms of the electromotive force, or voltage, E, of the source of electric energy, such as a battery. For example, I = E/R.

Method:

The circuit was set up as shown below. A table was drawn out and the results were recorded. To improve the accuracy, I decided to set up the circuit with the wire clipped to the metre rule and as stretched as possible. This will make it easier and more precise as I will not have to keep on holding the wire then putting the crocodile clips on. I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller ruler and the meter ruler can be accurate to +1mm. Make sure that the metre rule is actually one metre long and not one or two centimetres shorter. Next, move both the sides of the crocodile clips down five centimetres (so you get a ten centimetres) increase each time to record the results. To collect the data for my graph I have chosen to take a range of five lengths for one material. I have chosen a range of five as to plot an accurate graph; I will need at least five lines to mark on the graph if I want to make precise and reliable results, each with 10 results, to see if there are any patterns and trends. I have also chosen to take at least one repeat at each length and then take an average, to get reliable results. The lengths that I have chosen are as follows: 100cm to 20cm in 20cm steps length of wire. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results. I will also vary the voltage in this experiment, as to show what effect that would have. This means taking the readings off a voltmeter as that would be more accurate than the gauge on the PSU. Record the results with 0.1V jumps from 0V to 1V, any higher and the wire may start to burn with the 10cm length were using. We will try to take at least one repeat for each voltage. The results will be plotted as in the table below:

Aim:

To investigate the factors affecting the resistance of a wire varying the length and the voltage and the type of material used.

Plan:

Equipment:

* Meter ruler

* PSU

* Amp meter

* Voltmeter

* Multi meter (used as Ohmmeter)

* Croc clips

* Wire, 100cm+ of Nichrome

Scientific Knowledge:

The scientific knowledge is based on Ohm's law, which states then relationship that the amount of steady current through a large number of materials is directly proportional to the potential difference, or voltage, across the materials. Thus, if the voltage V (in units of volts) between two ends of a wire made from one of these materials is tripled, the current I (amperes) also triple; and the quotient V/I remains constant. The quotient V/I for a given piece of material is called its resistance, R, measured in units named ohms. The resistance of materials for which Ohm's law is valid does not change over enormous ranges of voltage and current. Ohm's law may be expressed mathematically as V/I = R. That the resistance, or the ratio of voltage to current, for all or part of an electric circuit at a fixed temperature is generally constant had been established by 1827 as a result of the investigations of the German physicist George Simon Ohm.

Alternate statements of Ohm's law are that the current I in a conductor equals the potential difference V across the conductor divided by the resistance of the conductor, or simply I = V/R, and that the potential difference across a conductor equals the product of the current in the conductor and its resistance, V = IR. In a circuit in which the potential difference, or voltage, is constant, the current may be decreased by adding more resistance or increased by removing some resistance. Ohm's law may also be expressed in terms of the electromotive force, or voltage, E, of the source of electric energy, such as a battery. For example, I = E/R.

Method:

The circuit was set up as shown below. A table was drawn out and the results were recorded. To improve the accuracy, I decided to set up the circuit with the wire clipped to the metre rule and as stretched as possible. This will make it easier and more precise as I will not have to keep on holding the wire then putting the crocodile clips on. I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller ruler and the meter ruler can be accurate to +1mm. Make sure that the metre rule is actually one metre long and not one or two centimetres shorter. Next, move both the sides of the crocodile clips down five centimetres (so you get a ten centimetres) increase each time to record the results. To collect the data for my graph I have chosen to take a range of five lengths for one material. I have chosen a range of five as to plot an accurate graph; I will need at least five lines to mark on the graph if I want to make precise and reliable results, each with 10 results, to see if there are any patterns and trends. I have also chosen to take at least one repeat at each length and then take an average, to get reliable results. The lengths that I have chosen are as follows: 100cm to 20cm in 20cm steps length of wire. I have chosen these lengths because they are easily measured by the meter ruler and give a good range of results. I will also vary the voltage in this experiment, as to show what effect that would have. This means taking the readings off a voltmeter as that would be more accurate than the gauge on the PSU. Record the results with 0.1V jumps from 0V to 1V, any higher and the wire may start to burn with the 10cm length were using. We will try to take at least one repeat for each voltage. The results will be plotted as in the table below: