# Relationship between the current and voltage.

Relationship between the current and voltage

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. Examples of these are Silicon, and Germanium.

Resistance

Ohmic Conductors Non-Ohmic Conductors

Obey Ohms Law Don't obey Ohms Law

Metals & Alloys Semi-Conductors

Resistance Increases with temperature Resistance decreases with temperature

At very low temperatures it becomes Since the resistance decreases with
a Superconductor temperature, they are called thermistors

Superconductors
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.

## Current

We could measure the amount of charge flowing in an electric current by counting the number of electrons, which pass by.
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.
The potential difference, (p.d), or the voltage of the battery measures this energy difference. 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)
0 0
0.45 0.23
0.52 0.26
0.58 0.28
0.8   0.4
1.0    0.49
1.35 0.63
1.55 0.74
1.8 0.89

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, ...