Discussion Forum

A condenser of capacitance  C is fully charged by a 200V supply. It is then discharged through a small coil of resistance wire embedded in a thermally insulated block of specific heat 250 J/kg-K and of mass 100 g. If the temperature of the block rises by 0.4 K, then the value of  C is 

Answer:

Explanation:

 The energy stored in the capacitor

$U= \frac{1}{2}CV^{2}=\frac{1}{2}C\times(200)^{2}=2 C\times 10^{4} J$

 This  energy is used to heat up the block 

Let  $\triangle\theta$ be the rise in temperature , then  heat energy

 $Q=ms\triangle\theta=0.1 \times 250\times0.4=10 J$

 Now  $2 C\times 10^{4}=10$

 $\Rightarrow$     $C= \frac{10}{2\times 10^{4}}=5\times 10^{-4}=500\mu F$