Question

(a
Derive the relation for the equivalent resistance when three
resistors of resistances R1, R2 and Rg are connected in parallel.
Find the minimum resistance that can be made using four
resistors, each of 20 22.​

Answer 1

Explanation:

(i) Total potential difference across a combination of resistors in series is equal to the sum of potential difference across the individual resistors.

V = V1 + V2 + V3

Let I be the current in the circuit. The current through each resistor is also I. It is possible to replace the three resistors joined in series by an equivalent resistor of resistance R. Applying Ohm's law,

V = IR

On applying Ohm's law to the three resistors respectively we further have

V1 = IR1

V2 = IR2

V3 = IR3

But V = V1+ V2 + V3

IR = IR1 + IR2 + IR3

(ii) Power rating of electric iron = 1kW = 1000 W

V = 220 V

P = VI

Hence , a fuse of rating 5A can be used because it can bear the current.