Theory+ Problem 1 on heat transfer through extended surfaces fin with insulated end

1. Which are the important formulae for heat conduction through extended surfaces with condition fin with insulated end?

2. Solve 1 Problem with condition Fin with insulated end.

Consider a transistor, idealised as a long cylinder of radius 1 mm and length 1.5 cm. On this a sheath of 1 mm thickness ( K= 0.1 W/mK) is put. Rating of transistor is 150 mW, and if the transistor is to function properly , it's surface temperature at radius 1mm should not exceed 80°C. If ambient air is 30°C (h = 15 W/m^2 K), how much heat can be dissipated into the atmosphere by three brass leads (K= 120 W/mK) Suppose we use circular wire leads of 0.3 mm diameter , what should be the length of these leads exposed to atmospheric air?

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