Relationship between the current and voltage
Aim: To investigate the relationship between Current and Voltage
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.
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
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.
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)
I = Q/t
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
Pd. (v) Current (I)