Ohms Law in Electrical Circuits

OHMS LAW

When a voltage is applied to a closed circuit, it causes flow of electrons and a current in the circuit. The resistance of the circuit opposes the flow of current. The actual value of the current flowing depends on the applied emf and resistance in the circuit, the relationship is given by ohm's law.

Statement of ohms law:

The potential difference (or) voltage across any two ends of a conductor is directly proportional to the current flowing through it, provided that the temperature of the conductor remains constant.

Mathematically, we can write,

V α I (Temperature is constant)

V = IR

Where

R is constant, becomes the resistance

V is in volts and

I is in amperes.

Limitations:

(i) It cannot be applied to non metallic conductors.

(ii) It cannot be applied to non linear devices such as zener diode, voltage regulator,etc.

(iii) It is applicable for constant temperature only. If the temperature changes, this law cannot be applied.

Example: 1

An electric heater draws 8A from 250V supply. What is its power rating?

Also find the resistance of the heater element.

Power rating = V.I

= 250 × 8

= 2000 W

Resistance = V/I = 250/8 Ω

= 31.25 Ω

Example: 2

A 5Ω resistor has a voltage rating of 100 V. What is its power rating?

P = V²/R

= 100²/5

=2000 W