Relationship Between The Current And Voltage Essay

Relationship Between The Current And Voltage Essay, Research Paper

Aim: To investigate the relationship between Current and Voltage

Scientific Knowledge The current and voltage of an electric circuit, is given by the formula V=IR. This is known as Ohms. Ohm´s Law is only applicable, when the temperature of the resistor is kept constant. Therefore Ohms law is only applicable to Ohmic conductors. An example of Ohmic conductors are metals and alloys at constant temperatures. Anything that doesn´t obey Ohms law, are know as non-Ohmic Conductors. An example of these are Silicon, and Germanium. Resistance Ohmic ConductorsNon-Ohmic Conductors

Obey Ohms LawDon’t obey Ohms Law

Metals & AlloysSemi-Conductors

Resistance Increases with temperatureResistance decreases with temperature

At very low temperatures it becomes Since the resistance decreases with

a Superconductortemperature, they are called thermistorsSuperconductors

At very low temperatures, atoms hardly vibrate at all.

Therefore the resistance is almost 0 Ohms, and the conductors are very good.

These are Superconductors. The resistance of a component can also be calculated, by the formula, R =KL/A.

This is where the cross sectional area is inversely proportional to the resistance, and the length, of the resistor, is directly proportional to the resistance. K is a constant in the formula, and is also know as P. This is the resistivity of the resistor. Current We could measure the amount of charge flowing in an electric current by counting the number of electrons, which pass by. However, electrons have only a tiny charge. Instead the unit for charge is the coulomb (C). One coulomb is the charge on six million million million electrons.

Electric currents are measured in amperes, or amps. When the current is 1 amp, the flow of charge is 1 coulomb, per second. When the current is 2 amps, the flow of charge is two coulombs per second.

Current (I) = charge flowing (Q)

time (t)

I = Q/t

Voltage In an electrical circuit, the battery provides the electrons with electrical potential energy. It turns chemical energy from the materials in the cell, into electrical energy, in the electrons. The electrons move through the circuit from the negative terminal where they have high electrical potential energy towards the positive terminal. When the electrons reach a bulb, they lose some of their electrical potential energy. This lost energy is then turned into heat and light. Finally, the electrons return to the positive terminal of the battery with less energy. Therefore, there is a difference in electrical potential energy between the negative and positive terminals of the battery.

This energy difference is measured by the potential difference, (p.d), or the voltage of the battery. The greater the voltage of the battery, the more energy it can provide.

The potential difference is measured in volts, (V), using a voltmeter. The voltmeter is connected in parallel, to the component desired to measure the voltage going through it.

A battery with a voltage of 1 volt gives 1 joule of energy, to each coulomb of charge that passes round the circuit. Voltage (V) = Energy per unit charge = Energy supplied (E)

Charge flowing (Q) V = E/Q and E = V x Q As charge flowing = Current x time ; Q = I x t If I then substitute Q in the equation E =V x Q We get E = V x I x t Energy = Voltage x Current x time E = Vit

Preliminary Experiment

Results

Pd. (v)Current (I)

00

0.450.23

0.520.26

0.580.28

0.80.4

10.49

1.350.63

1.550.74

1.80.89

The results from this experiment tell me that when the resistance is kept constant, the (V,I) graph drawn will have a positive gradient and be a straight line. This has helped me in my prediction. From the experiment, I have also learned of the necessity, to carry out repeated experiments. In the results above, I failed to do so, and that explains why the graph isn´t as straight as it should be. Plan

For this experiment, I will have one independent variable. This is going to be the voltage. As the voltage of the circuit is going to vary, there will be at least two dependant variables. These are going to be the current flowing through the circuit, and for the bulb experiment, the brightness of the bulb, is also classified as a dependant variable.

I will investigate the relationship between the current and voltage, for a wire wound resistor, ad a light bulb, as well as the relationship between the resistance and % of light emitted by the bulb. As stated above, the only independent variable will be the potential difference off the circuit. This will be controlled using a potentiometer.

The resistance of the components will be a constant, except for the light bulb. As this will light up, the resistance will also vary.

As I predict the graph for the light bulb to be a curve, I will receive about 12 results for each different component. These will be carried out at suitable intervals, depending on the component. The experiment will be carried out three times to ensure that average readings can be obtained.

The experiment will be carried out fairly, s possible. Averages w

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