Electric current, the flow of electric charge, usually in the form of electrons. In a circuit, it is measured using an ammeter, and the SI unit of measurement is the ampere (A). It may be direct current (D. C. ), in which case the charge flow is one way, as from a battery. Or it may be alternating current (a. c. ), as from a mains supply. Here, the charge flows alternately backwards then forwards in a circuit many times every second. The equation for current is I=Q/T; A=C/S; current= charge/time.
Resistance Resistance, the ratio of the potential difference (p. d.or voltage) across a conductor to the electrical current which flows through it as a result. The unit of measurement is the ohm (O), this being the resistance of a conductor requiring a potential difference of 1 volt across its ends to produce a current of 1 ampere. For a given metal conductor at constant temperature the value is the same whatever the current (Ohm’s law), but rises if the temperature rises the equation for Ohms law is V=IR; Voltage (p. d. ) =current x resistance. Any conductor possessing resistance gives off heat when a current flows through it. The effect is described by Joule’s law.
The equation for resistance is R=V/I; ? =V/A; resistance= voltage (p. d. )/current. IV graphs compare the current to the voltage of various conductors. Here are 4 main IV graphs. Resistor, the current is proportional to the voltage. Wires, different wires have different resistances hence the different slopes. Filament bulb, as the temperature of the filament increases, the resistance increases hence the curve. Diode, the current will only flow in one direction as shown. Electrical conduction is the flow of electric current through matter. It occurs in three types of matter.
In metals there is a bulk movement of electrons in the direction of an applied electric field. For a current to flow the electrons must be free to move and this occurs only if there are available energy levels just above the existing energy level of the electron; if these energy levels are too far above the existing levels then the material is an insulator, most metals make good conductors and most non-metals are good insulators.. In semiconductors the ability of the material to conduct is much less than in metals, but unlike metals, it increases as the temperature rises (band theory).
In solutions an electric current can be carried by electrolytes, as in electrolysis. Voltage Potential difference (p. d. ) is the difference in electric potential between two points in an electric field. It is defined by the work that must be done to move a unit charge from one to the other. In the SI system it is measured in joules per coulomb, or volts (V), and potential difference is commonly called voltage. The equation for voltage is V=E/Q; V=J per second/C; voltage (volts) = energy (j/s)/charge (coulombs). Factors affecting the resistance in a wire 1.
Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance. 2. Material: The type of material will affect the amount of free electrons which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available.
If the material has a high number of atoms there will be high number of electrons causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase. 3. Wire length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase.
4. Wire width: If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be fewer collisions. Aim: To investigate a factor affecting the resistance of a wire. Prediction: I predict that the longer the wire the more/higher the resistance will be. I think this because the longer the wire is, the more the electrons will have to travel and this means that there will be more collisions occurring.
I also predict that the wider the wire the lower the resistance will be. I assume because there will be more space for the electrons to move. In addition I also think that higher the temperature the higher the resistance because the atoms will start to vibrate due to the amount of excess energy, and this movement will cause the atoms to move into the electrons paths causing more collisions. Preliminary: For my preliminary results, I will test the wire (constantan) at 5 volts. I will test the wire at two lengths; these lengths will be 10cm and 100cm. The diameter of the wire will be 36 SWG.
I will also be using a meter ruler, an ammeter and a voltmeter. The reason I chose the two lengths was that they were the two extremes for my investigation. This is how my apparatus will be step up:- Preliminary Method- I will set up the apparatus as in the diagram and then take three readings from the voltmeter and ammeter for length. I will then find the resistance for each reading for each length. I will then take the average for reading of the ammeter and voltmeter and find the average resistance.