The circuit shown below is working as a $8Vdc$ regulated voltage source. When $12\text{}V$ is used as input, the power dissipated (in $mW$ )in each diode is; ( considering both Zener diodes are identical)____

Total voltage drop across both resistors is 4V.

Current in the circuit $i=\frac{4}{400}=\frac{1}{100}A$.

Voltage drop across each diode is 4V. 

So, power dissipated in each diode is $p=vi$    $=4\times \frac{1}{100} =40\times {10}^{-3} W =40mW$