Two rods of same material have same length and area. The heat Q flows through them for 12 minutes when they are joint side by side. If now both the rods are joined in parallel, then the same amount of heat Q will flow in :

Step-by-step solution

When rods are joined in series then heat flow aligned & Q₁= A (T₁-T₂ ) t₁ l₁ K₁ + l₁ K₂ & = A (T₁-T₂ ) t₁ l K₁ + l K₂ = A (T₁-T₂ ) t₁ l K 2 aligned When rods are joined in parallel aligned Q₂ & = (K₁ A+K₂ A ) (T₁-T₂ ) t₂ l & = 2 K A (T₁-T₂ ) t₂ l Q₁ & = Q₂ (given) aligned t₂= t₁ 4 = 12 4 =3 ~min