OHM'S Law

OHM'S LAW

Ohm's law states that in a linear network, at constant temperature the voltage across the conducting material is directly proportional to the current flowing through the material.

i.e., V ∞ I

or V = IR.

From this the values of I and R can be determined from the following:

Limitations of Ohm's Law

(1) Ohm's law is applicable only for metallic conductors maintained at a constant temperature. This law is not applicable if the temperature changes.

(2) Ohm's law is not applicable to all non-metallic conductor.

(3) If is also not applicable to non-linear devices. Such as diodes, transistors and other semiconductor devices.

Example 1.1: Find the voltage drop across a 10 k resistor of the current flowing through it is 1 mA.

Given: R = 10 kQ

I = 1 mA

V = IR = 1 x 10-3 x 10 x 103

= 10 V.

Example 1.2: Find the value of cross resistance R in the circuit shown in the figure below if the ammeter measures 1 mA and voltmeter measures 2 V.

Example 1.3: A bulb is rated as 230 V, 1 A. Find the resistance of the filament.

Given: V = 230 V, I = 1 A