Basic Electricity Law: Ohm’s Law

Ohm’s law states that at constant temperature, the current between two points of a conductor is directly proportional to the voltage (potential difference) across the two points.

I α V

Introducing the constant of proportionality, the resistance (R) we arrive at the mathematical equation that describes Ohm’s Law relationship as:

Where:

I = the current through the conductor in units of amperes (A)

V = the voltage measured across the two points of the conductor in units of volts (V), and

R = the resistance of the conductor in units of ohms (Ω).

From the mathematical relationship above, Ohm’s law can be restated thus:

At constant temperature, the current flowing through any two point of a conductor is directly proportion to its potential different (voltage applied) and inversely proportion to its resistance.

Ohm’s law parameters

Solved Examples on Ohm’s Law

Example 1

Determine the current flowing through a conductor if voltage of 24V is placed across a 400ohm resistor.

SolutionVoltage (V) = 24V

Resistance (R) = 400 Ω

I =   = 0.06A = 60mA

Example 2

Find the potential difference across two points of a conductor if the a current of 10mA flows through a resistance 700Ω

Solution

V = IR = 0.01 x 700 = 7V.

Example 3

From the circuit below, calculate the current (I), Conductance (G) and power dissipated (P)

Solution

Power dissipated (P) = VI = I² R = (0.006)² x 6000 = 216mW

Example 4

Calculate the current through the resistor and the power dissipated if a voltage of 16Sinθ t is connected across a load of resistance 2kΩ.

Solution

Power dissipated (P) = VI = 16Sinθt x 8Sinθt = 128Sin²(θt) mW

Example 5

At a voltage of 5Cosθ V, a resistor absorbs an instantaneous power of 25Cos²θ mW. Calculate:

1. The value of the current (I) flowing through the circuit.
2. The value of the resistor (R)

Solution