Question 6 - Past Year - 5 Mark Questions - Chapter 12 Class 10 - Electricity

(a) Three resistors R1, R2 and R3 are connected in parallel and the combination is connected to a battery, ammeter, voltmeter and key. Draw suitable circuit diagram and obtain an expression for the equivalent resistance of the combination of the resistors.

(b) Calculate the equivalent resistance of the following network:

Answer:

(a)

Note - In case of parallel, the total resistance is always less than the resistance of the individual resistors.

The net resistance produced is lowest when resistors are connected in parallel.

(b)

Let R’ be the equivalent resistance of the two 20 ohm resistors connected in parallel.

Therefore,

1 / R’ = 1 / 20 + 1 / 20

          = 2 / 20

R’ = 20 / 2 = 10 ohm 

Let R be the equivalent resistance of the entire network. 

The 10 ohm resistor and R’ are in series.

Therefore, 

R = R’ + 10 ohm = 10 + 10 = 20 ohm

Therefore, the equivalent resistance of the given network is 20 ohm.