Ohm’s Law Resistance and Resistors

Resistance is the difficulty applied by the conductor to the current flowing through it. Each material has different resistance. We show resistance with R and unit of it is ohm (Ω).

1 Ω=resistance of the conductor when 1 A current flows under the 1 V potential difference. Resistance is represented with the following picture in circuits;

Rheostat

Rheostat is a kind of device used to vary existing resistance. It is shown in the circuits as;

Resistance of the conductor depends on;

· Types of the material or electrical resistivity of the material. It is shown with Greek letter ρ. Resistance of the material is linearly proportional to electrical resistivity.

· Length of the material (l). Resistance is linearly proportional to the length of the conductor.

· Cross sectional are of the conductor. Resistance is inversely proportional to the cross sectional area.

· Temperature. Temperature shows different effects with respect to the type of material.

We write resistance formula with the explanation given above as;

Ohm’s Law

Ohm’s law gives the relation between voltage, current and resistance. According to Ohm, current in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance of the conductor. We can summarize this explanation with following formula;

If we take resistance of the conductor constant, then potential difference and current of the system changes linearly as shown in the following graph;

Example: Potential difference vs. Current graph of a conductor is given below, Find the behavior of resistance in intervals I, II and III.

Ohm’s law states that V=I.R

• In the first interval, since the potential difference and current are linearly increases then resistance of the system becomes constant.

• In the second interval, potential difference is constant however, current increases. This can be possible by decreasing in the amount of resistance.

• In the third interval, current is constant, however, potential difference increases. This can be possible by increasing in the amount of resistance.

Electric Current Exams and Solutions