Two rods of same length, area of cross-section and material transfer a given amount of heat in 12s, when they are joined end to end (i.e. in series).But when they are joined in parallel, they will transfer same heat under same conditions in
3 s
Let R=1kACase I (series)H1=T1−T2RsT1−T22RCase II (parallel)H2=T1−T2RpT1−T2R2⇒2H1=H22⇒H2=4H1We have,H1t1=H2t2H1(12)=4H1t2t2=3s.