Two rods of same material have same length and area. The heat $\Delta Q$ flows through them for $12\,minutes$ when they are jointed in series. If now both the rods are joined in parallel, then the same amount of heat $\Delta Q$ will flow in ........ $\min$
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$\Delta Q=\frac{\Delta T}{R} t$
in series $\mathrm{R}_{\mathrm{eq}}=2 \mathrm{R},$ in parallel $\mathrm{R}_{\mathrm{eq}}=\mathrm{R} / 2$
$\Delta Q=\frac{\Delta T}{2 R} \times 12=\frac{\Delta T}{R / 2} t$
$\Rightarrow \frac{\Delta \mathrm{T}}{2 \mathrm{R}} \times 12=\frac{\Delta \mathrm{T}}{\mathrm{R} / 2} \mathrm{t}$
$\Rightarrow \mathrm{t}=3$ minutes
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