Question

Sanya performed an experiment of obtaining characteristic curves of a junction diode. When she forward biased it, she found that beyond forward voltage V = Vk, the conductivity is very high. When she reverse biased the diode she found that a very small current (of about a few microamperes) flows in the diode. It remained constant even though she varied the voltage.

(i) In Figure 1 below, which one of the diodes is forward biased?

Figure 1

(ii) What is meant by a saturation current?

(iii) When applied voltage during forward bias is small, why does no current flow in the diode?

(iv) The circuit shown in Figure 2 below contains two diodes, each with a forward resistance of 50 Ω and with infinite resistance during reverse bias. If the battery voltage is 6V, then calculate the current through the 100 Ω resistance.

Figure 2

Answer 1

(i) D₂ is forward biased.

(ii) It is that current which remains constant even on increasing the p.d.

(iii) Due to potential barrier or barrier p.d.

(iv) Ignoring D₂ as it is reverse biased and offers infinite resistance, By Ohm's law,

`I = E/(R∗ + R∗)`

= `6/(50 + 150 + 100)`

= `6/300`

= 0.02 A