Question

A diode made of silicon has a barrier potential of 0.7 V and a current of 20 mA passes through the diode when a battery of emf 3 V and a resistor is connected to it. The power dissipated across the resistor and diode are
(A) 0.046 W, 0.014 W
(B) 4.6 W, 0.14 W
(C) 0.46 W, 0.14 W
(D) 46 W, 14 W

Answer 1

barrier potential is property of the material and for silicon it is 0.7V while for germanium it is 0.3V. Diodes are made from semiconductors and their conductivity lies between conductors and insulators. Here the diode is connected to an external source and we need to find power dissipated across it

Complete step by step answer:
Given barrier potential, ${{V}_{D}}=0.7V$
I= 20 mA
=0.02 A
External source emf, ${{V}_{B}}=3V$
The barrier potential is the minimum amount of potential which needs to be applied in order for current to move. So, it will be subtracted from the potential applied.

& {{V}_{net}}=(3-0.7)V \\\ & =2.3V \\\ \end{aligned}$$ Now to calculate power using the formula $$P={{V}_{net}}I$$ $$=2.3\times 0.02$$ =0.046 W Now we want to calculate the power dissipated across the resistor, $$P={{V}_{D}}I$$ =0.014 W So, the power dissipated across the resistor is 0.014 W Hence the correct option is (A) Additional Information: The potential barrier in the diode is the barrier in which the charge requires additional force for crossing the region. The value of barrier potential lies between (0.3 – 0.7) V **Note:** The value of current is to be taken in Ampere and potential difference in volts. Power is dissipated in overcoming the barrier potential and also across the resistance.