Measure the value of the current flowing in the circuit with help of the ammeter. Note its values in your book as I.

• What do you notice?

Observe figure 17. In this figure the bulbs are shown as resistors with symbols.
In series connection of resistors there is only one path for the flow of current in the circuit. Hence, the current in the circuit is equal to I.

According to Ohm’s law,
potential difference across R₁is, V₁=IR₁
potential difference across R₂is, V₂=IR₂
potential difference across R₃is, V₃=IR₃

Let R_eqis the equivalent resistance of the combination of resistors in series.

• What do you mean by equivalent resistance?

If the current drawn by a resistor is equal to the current drawn by the combination of resistors then the resistor is called as equivalent resistor (provided the source in the circuit is constant).
So,we have V=IR_eq
Substituting the values of V₁, V₂, V₃ and V in the equation (1), we get
IR_eq = IR₁ +IR₂ +IR₃
R_eq = R₁+ R₂+ R₃
From the above equation you can conclude that the sum of individual resistances is equal to their equivalent resistance when the resistors are connected in series.

• What happens when one of the resistors in series breaks down?

When one of the resistors in series breaks down, the circuit becomes open and flow of current cannot take place in the circuit. This is the reason why household electrical appliances are not connected in series.

• Can you guess in what way household wiring has been done?
  Let us see