Fair testing
To make this experiment fair I must only change on aspect of the experiment. I will be changing the length of the wire and nothing else. All other aspects will stay the same for the duration of the experiment, such as voltage and current. If more than one aspect were changed the experiment would not give accurate results and would be of no use.
Diagram of experiment
The experiment will work by electricity passing through the constantan. The length of the constantan will change the amount of resistance there is. The longer and thinner the wire is the more resistance it has because of the amount positive ions the electrons will hit as they pass through the wire. Resistance is the property of any object or substance, resisting or opposing the flow of an electrical current. The amount of resistance in an electric circuit determines the amount of current flowing in the circuit at any voltage in the circuit. They can then show the amount of electrons passing through the wire.
The resistance is found by using ‘Ohms Law’. Ohms law, named after it discoverer, Georg Ohm (a German physicist). Ohms law states that the amount of current flowing through a conductor is directly proportional to the electromotive force applied between the ends of the conductor. Resistance is defined as the ratio of the electromotive force to current, this creates the formula R= V/I, where I is the current in amps, and V is the voltage. Ohms law works in both direct current (DC) and alternating current (AC), the circuit I am using though is DC.
The higher the voltage the more resistance that will occur due to the amount of electrons hitting the positive ions, if there are enough collisions the energy from this can make the wire become extremely hot and glow.
Resistance in wires can be shown by the diagram beneath
The resistance process ‘slows down’ the flow, resistance is a measure of how easy the electrons can move through the metal, a lower resistance means that electrons can move more easily.
The temperature of the metal wire can affect the resistance. The heat can affect the resistance because a higher temperature causes the positive ions to vibrate, this vibrating action means that an electron has a larger chance of hitting a positive ion, thus the resistance is higher. To assure that this problem does not occur in my experiment I must make sure that the wire isn’t subject to high voltage, because that will result in a higher temperature which will affect my results, when I do the experiment I must also only put the power on for the duration needed to collect the result.
Prediction
I predict by the use of the information that I have found out that the longer the constantan wire is the more resistance that will be created. My reason for this is that the further the electrons have to pass in wire the more positive ions they will hit as they pass through, therefore twice the length of wire means twice the amount of positive ions and twice the amount of collisions. This results in a larger resistance than a shorter piece of constantan. The resistance is therefore going to decrease as I change the length of constantan I am using from 100cm to 10cm. I predict that the resistance at 50cm will be half the resistance at 100cm and the resistance at 10cm will be a tenth of the resistance at 100cm.
Resistance is the Greek letter omega, Ω
Microsoft® Encarta® Encyclopedia 2003. ©
Current flows in an electric circuit in accordance with several definite laws. The basic law of current flow is Ohm's law, named after its discoverer, the German physicist Georg Ohm. Ohm's law states that, over a wide range of circumstances and materials, the amount of current flowing through a conductor is directly proportional to the electromotive force applied between the ends of the conductor. If resistance is defined as the ratio of electromotive force to current, then V = IR, where I is the current in amperes, V is the electromotive force in volts (see Electrical Units), then Ohm's law is equivalent to saying that R (which is measured in ohms) is a constant in the specified circumstances. A material for which this holds true is described as ohmic. Ohm's law can apply to electric circuits for both direct current (DC) and alternating current (AC), but additional principles must be invoked for the analysis of complex circuits and for AC circuits involving inductances and capacitances.
A series circuit is one in which the devices or elements of the circuit are arranged in such a way that the entire current passes through each element without division or branching into parallel circuits.
When two or more resistances are in series in a circuit, the total resistance may be calculated by adding the values of such resistances. If the resistances are in parallel, the total value of the resistance in the circuit is given by the formula
Direct Current Resistivity is useful for the following:
- Characterize subsurface hydrogeology
- Determine depth to groundwater
- Map stratigraphy
- Map clay aquitards
- Map salt-water intrusion
- Map vertical extent of certain types of soil and groundwater contamination
- Estimate landfill thickness
- Determine depth to bedrock/overburden thickness
- Map faults
- Map lateral extent of conductive contaminant plumes
- Delineate disposal areas
Electrical or direct current methods measure the bulk resistivity of the subsurface to determine geologic structure and/or physical properties of the geological materials. An electrical current is introduced directly into the ground through current electrodes. The resulting voltage potential difference is measured between a pair of potential electrodes. The current and the potential electrodes are generally arranged in a linear pattern. The apparent resistivity is the bulk average resistivity of all soils and rock influencing the flow of current.
Resistivity Calculation
The electrical of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (). Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as
= x /
For a wire of length L = m = ft
and area A = cm^2
corresponding to radius r = cm
and diameter inches for comparison
with resistivity = = x 10^ ohm meters
will have resistance R = ohms.
Enter data and then click on the quantity you wish to calculate in the active formula above. Unspecified parameters will default to values typical of 10 meters of #12 copper wire. Upon changes, the values will not be forced to be consistent until you click on the quantity you wish to calculate.
The factor in the resistance which takes into account the nature of the material is the resistivity . Although it is temperature dependent, it can be used at a given temperature to calculate the resistance of a wire of given geometry.
www.hyperphysics.phy-astr.gsu.edu/hbase/electric/resis.html