#### Physics (NTSE/Olympiad)

# 1. Electricity

__Ohm's Law __

**Ohm's Law ** **Definition : **According to the Ohm’s law at constant temperature, the current flowing through a conductor is directly proportional to the potential difference across the conductor.

Thus, if I is the current flowing through a conductor and V is the potential difference (or voltage) across the conductor, then according to Ohm’s law.

I ∝ V (when T is constant)

or, I = V/R ...(i)

where R is a constant called the

**resistance of the conductor.** Equation (i) may be written as, -

V = I x R ...(ii)

** Unit of resistance : ** The SI unit of resistance (R) is ohm. Ohm is denoted by the Greek letter omega (Ω).

From Ohm’s law, R = V/I

Now, if, V = 1 Volt and I = 1 Ampere

Then,

Thus, 1 ohm is defined as the resistance of a conductor which allows a current of 1 ampere to flow through it when a potential difference of 1 volt is maintained across it.

**Results of Ohm’s Law ** Current flowing through a conductor is directly proportional to the potential difference across the conductor.

When the potential difference in a circuit is kept constant, the current in inversely proportional to the resistance of the conductor.

I ∝ 1/R

The ratio of potential difference to the current is constant. The value of the constant is equal to the resistance of the conductor (or resistor).

V/I = R