Current-Voltage Relationships and Ohm’s Law – Learn
Current, Voltage and Resistance are common terms that are used to describe electricity in circuits.
Current is the amount of charge that passes through a point in a conductor each second. The symbol for current is I and the unit is amps (A).
Voltage (potential difference) is the work done to move a charge against an electric field between two points. The symbol for voltage is V and the unit for voltage is volts (V)
Resistance is a measure of how difficult it is for current to flow through a material. The symbol for resistance is R and resistance is measured in ohms (Ω). There are several factors that effect the resistance of a conductor:
- Length – If the material has a longer length, this will result in a higher number of collisions with other ions within the conductor, increasing the resistance and making it harder for the current to flow.
- Cross-sectional area – With a large cross-sectional area, there is less chance of collisions and the resistance will decrease.
- Temperature – Higher temperatures will result in an increased vibration of the ions, making the chances of electrons colliding higher and the resistance will increase.
Ohm’s law describes the relationship between current, voltage and resistance:
= the voltage (in V)
= the current (in A)
= the resistance (in Ω).
Ohmic and non-ohmic resistors:
Ohmic conductors obey Ohm’s law and have a constant resistance. The resistance of non-ohmic conductors varies for different voltages. Light bulbs are an example of a non-ohmic conductor. The resistance of light bulb increases as the temperature of the filament increases.
Ohmic and non-ohmic conductors can be explored by plotting a graph of current vs voltage. The graph for an ohmic conductor is a straight line. The resistance can be found from the gradient of the graph. The current vs voltage graph for a non-ohmic conductor is not a straight line.
What voltage will flow through a wire with a resistance of 1.5Ω to produce a current of 4A?
What is the resistance of a wire that produces a current of 8A when a voltage of 2V is applied?
Using and rearranging to give: