### Q.4:- Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –(a) 1:2 (b) 2:1 (c) 1:4 (d) 4:1

**Answer:-**

(c) Heat produced in the circuit is inversely proportional to the resistance

*R*.Let

*R*_{S}be the equivalent resistances of the wires if connected in series and*R*_{P }be the equivalent resistances of the wires if connected in parallelThen

*R*_{S}=R+R=2RAnd 1/

*R*_{P}= 1/R +1/R 1/

*R*_{P}= 2/ROr

*R*_{P}=R/2Now the ratio of heat produced is given by

= 1/4