Q4. What are the typical threshold (cut-in) voltages of germanium and silicon diodes?
About 0.2 V for germanium and about 0.7 V for silicon (NCERT page 337).
Q5. Why is a microammeter, not a milliammeter, used to measure the current of a reverse-biased diode?
The reverse current is only of the order of μA, far too small to read on a milliammeter (NCERT pages 336–337).
Q6. Assertion: below breakdown, the reverse current of a diode hardly changes as the reverse voltage is raised. Reason: the reverse current is limited by the number of minority carriers near the junction. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (NCERT pages 335–336).
Q7. A diode carries a reverse current of 3 μA at −15 V. Find its reverse resistance, V/I, as NCERT does in Example 14.4.
r = 15 V/3 μA = 5.0 × 106 Ω (worked as NCERT Example 14.4, page 337).
Q8. How does the width of the depletion region change in forward bias and in reverse bias?
It decreases in forward bias, as the barrier falls to V0 − V, and increases in reverse bias, as the barrier rises to V0 + V (NCERT pages 334–335).
Q9. The p-side of a diode is at −2 V and its n-side at −5 V. Is it forward or reverse biased?
Forward biased by the stated terminal potentials: the p-side is 3 V above the n-side. A real silicon p-n diode would normally draw a very large current at that voltage, so this is a polarity question, not a safe operating example. Relative potential determines the bias (NCERT page 334).