“Ohm’s Law states that the current through a metallic conductor at constant temperature is proportional to the potential difference. (p. d. ). Thus p. d. over current is constant. ” GCSE Text Book. What is resistance? Resistance is defined as voltage over current. The unit of resistance is the ohm (? ). So; Resistance = Background Information (Found in “Google. com”) Electricity in wired circuits consists of the flow of electrons. Current is the word used to describe this flow, and is measured in amperes.
Because positive and negative charge “dislike” being apart, current can only flow when a complete circuit exists: At least one closed loop for the electrons to run around. Current flows because of an electric potential-voltage-that exists in the circuit. An example of a source of voltage is a battery; here electrochemical reactions produce electric potential. Another example is a power generator powered by steam (a turbine) or by rushing water (hydroelectric generators). The former are examples of constant (DC) voltage sources (most flashlight batteries produce a constant 1.
5 volts) and the latter AC sources, where the voltage varies in a pattern like that of a sinus curve. Circuits are comprised of the interconnection of circuit elements. Each element is distinguished by the relation it imposes on the voltage across it and the current flowing through it. The voltage source produces a DC or AC voltage, and does so regardless of the current flowing through it. A straight line indicates a wire that has no voltage drop across it and allows current of any size to flow through it. Wires are used to interconnect circuit elements to form circuits. A resistor constrains its voltage and current to be proportional.
This relation amounts to the most famous circuit law: Ohm’s Law. (As stated above) V = IR R – resistance in ohms (? ) V – voltage (volts) I – current (amperes) Planning Outline My task is to investigate resistance. From the evidence seen above in the background information section I have started to make a plan. Basically, I’m going to make a circuit with various components and measure the resistance across a nickel chromium wire. I shall use different lengths. The I shall repeat the experiment on different gauges of wires and possibly on wires made of different materials. Apparatus Power Pack (DC) Multimeter (x2).
Rheostat Nickel Chromium Wires (x4… SWG 30, 28, 24,,22) Constantan Wire (x1… SWG 30) Copper Wire (x1… SWG 30) Manganane Wire (x1… SWG 30) 1 Meter rule Circuit Board Crocodile Clips Circuit Wires Diagram of circuit STRATEGY The Power Pack will be set to a DC supply. The circuit shall be set up as shown in the above diagram. The testing wires shall be fixed to the 1 meter long circuit board. The meter rule shall be placed along the testing wires and it shall be divided into ten sections of ten centimeters.
The crocodile clips shall be placed at ten centimeters from the end of the wire…(see diagram). The power pack shall be switched on and a reading on the Ammeter and Voltmeter shall be taken down. Then the rheostat shall be moved to take a different reading. This shall be repeated three times for each length of wire to ensure that the test is fair. Then the crocodile clips shall be moved by another ten centimeters from the end of the wire. Another three readings shall be taken and the crocodile clips shall be moved another ten centimeters. This process shall be repeated until the whole length of the wire has been covered then the same test shall be done on a different wire.
Once the whole wire has been tested, the crocodile clips shall be placed 1mm apart on a section of the wire. The resistance across this section shall be considered negligible. The use in this test is to determine how much resistance there is in the circuit wires, connected to the test wires. This shall be my “control”. This will ensure that the test is fair. The experiment shall be finished when all the wires on the apparatus list have been tested. Variables (key factors) 1. Temperature 2. Length of Wire (Independent Variable) 3. Width of Wire (Independent Variable) 4. Type of Wire (Also Independent Variable).