Characteristic curves of a p-n junction and a Zener diode — NEET & JEE Questions

Question 1 · difficulty L1 · recall

The forward characteristic of a p-n junction shows a rapid current rise after

• A. the knee voltage
• B. reverse breakdown only
• C. zero current at all voltages
• D. the Zener voltage in forward bias always

Question 2 · difficulty L1 · understanding

The reverse current of an ordinary diode before breakdown is

• A. larger than the forward current at the same voltage magnitude
• B. small
• C. infinite
• D. exactly equal to forward current

Question 3 · difficulty L2 · understanding

A Zener diode's regulation region appears on the I-V graph in

• A. forward-bias linear region only
• B. zero-bias point only
• C. reverse breakdown
• D. a region of no current and changing voltage

Question 4 · difficulty L2 · application

In plotting a diode characteristic, a series resistor is used mainly to

• A. make the diode perfectly ohmic
• B. remove the need for voltage measurement
• C. change the sign of charge carriers
• D. limit current and protect the diode

Question 5 · difficulty L2 · understanding

In the forward characteristic of a silicon p-n junction diode, the current begins to rise sharply after the threshold (knee or cut-in) voltage, which is about

• A. 0.1 V
• B. 0.3 V
• C. 0.7 V
• D. 1.5 V

Question 6 · difficulty L3 · application

To plot the forward I-V curve accurately, the voltmeter should measure

• A. voltage directly across the diode
• B. only battery emf regardless of resistor drop
• C. current through the diode
• D. resistance of the ammeter

Question 7 · difficulty L3 · application

A diode curve shows about 0.7 V at a sharp forward-current rise. The device is most consistent with

• A. an ideal resistor
• B. a silicon diode
• C. a glass prism
• D. a galvanometer coil

Question 8 · difficulty L3 · application

On the forward characteristic of a diode, increasing the voltage from 0.70 V to 0.80 V raises the current from 10 mA to 30 mA. The dynamic (AC) resistance of the diode in this region is

• A. 70 $\Omega$
• B. 27 $\Omega$
• C. 0.2 $\Omega$
• D. 5 $\Omega$

Question 9 · difficulty L3 · application

While tracing the characteristic curves of a p-n junction diode, a milliammeter is used for the forward-bias circuit and a microammeter for the reverse-bias circuit. Why?

• A. Forward current is of the order of milliamperes, while the reverse (saturation) current, carried by minority carriers, is only of the order of microamperes
• B. Reverse current is larger and would damage a milliammeter
• C. The two meters are interchangeable; either may be used
• D. The microammeter is needed because reverse voltage is small

Question 10 · difficulty L4 · analysis

On a Zener reverse characteristic, increasing current substantially while voltage changes only slightly indicates

• A. very large dynamic resistance
• B. no breakdown
• C. small dynamic resistance in breakdown
• D. forward open-circuit behaviour