Forward and Reverse Bias - UNSOLVED PRACTICE SET
Chapter: Semiconductor Electronics | Topic: Forward and Reverse Bias
FORWARD AND REVERSE BIAS - UNSOLVED PRACTICE SET
Topic: Forward and Reverse Bias
Multiple Choice Questions
Q1. In forward bias of a p-n junction diode:
- The p-side is connected to the negative terminal and the n-side to the positive terminal
- The p-side is connected to the positive terminal and the n-side to the negative terminal
- Both sides are connected to the positive terminal
- No external voltage is applied
Q2. In reverse bias of a p-n junction diode:
- The depletion region width decreases
- The depletion region width increases
- Majority carriers flow across the junction easily
- The diode offers very low resistance
Q3. The forward current in a diode increases exponentially with voltage according to:
- I = Iโ e^(V/V_T)
- I = Iโ (e^(V/V_T) โ 1)
- I = Iโ e^(-V/V_T)
- I = Iโ V/V_T
Q4. The reverse saturation current in a diode:
- Increases rapidly with reverse voltage
- Is independent of temperature
- Is due to minority carriers and increases with temperature
- Is very large in silicon diodes
Q5. The knee voltage (cut-in voltage) for a silicon diode is approximately:
- 0.2 V
- 0.7 V
- 1.4 V
- 2.0 V
Q6. In reverse bias, the current is carried mainly by:
- Majority carriers
- Minority carriers
- Both majority and minority carriers equally
- No carriers
Short Answer Questions
Q7. What is forward bias? Draw a circuit diagram showing a diode in forward bias.
Q8. What is reverse bias? Draw a circuit diagram showing a diode in reverse bias.
Q9. Explain why the depletion region width decreases in forward bias and increases in reverse bias.
Q10. Why does a diode not conduct significantly until the forward voltage exceeds the knee voltage?
Q11. Draw the V-I characteristic of a p-n junction diode and label the forward bias region, reverse bias region, and breakdown region.
Q12. Why does the reverse saturation current double for approximately every 10ยฐC rise in temperature?
Long Answer Questions
Q13. Explain the working of a p-n junction diode in forward bias with a circuit diagram. Discuss how the applied voltage overcomes the potential barrier and how the current flows.
Q14. Explain the working of a p-n junction diode in reverse bias with a circuit diagram. Discuss the formation of the depletion region and the origin of reverse saturation current.
Q15. Draw and explain the complete V-I characteristics of a p-n junction diode. Discuss the forward bias region, reverse bias region, and the breakdown region (both Zener and avalanche breakdown).
Numerical & Application-based Problems
Q16. A silicon diode has a reverse saturation current Iโ = 10โปยนยฒ A at 300 K. The thermal voltage V_T = kT/e = 26 mV.
(a) Calculate the diode current when a forward voltage of 0.7 V is applied.
(b) Calculate the diode current when a forward voltage of 0.5 V is applied.
(c) Calculate the ratio of the two currents and explain why the diode is considered 'off' below 0.5 V and 'on' above 0.7 V.
(d) Calculate the dynamic resistance of the diode at 0.7 V forward bias.
Q17. A diode is connected in series with a resistor R = 1 kฮฉ and a voltage source V_s. The knee voltage of the diode is 0.7 V.
(a) If V_s = 5 V, calculate the current through the circuit in forward bias.
(b) If V_s = โ5 V, calculate the current through the circuit in reverse bias (assume reverse saturation current Iโ = 1 ฮผA).
(c) Draw the output voltage waveform across the resistor if V_s is a sinusoidal voltage with peak value 5 V.
Q18. In your school electronics lab, a student is testing diodes and building simple circuits.
(a) She has a silicon diode and a germanium diode. She connects each in series with a 100 ฮฉ resistor and a 2 V battery. Calculate the expected current in each case (knee voltage for Ge = 0.3 V, for Si = 0.7 V).
(b) The student then connects a diode in reverse bias across a 9 V battery. She measures a current of 50 nA at 25ยฐC. Predict the current at 75ยฐC, assuming it doubles every 10ยฐC.
(c) She builds a simple circuit to protect an LED from reverse voltage damage. Draw the circuit showing how a diode can be used for this protection and explain its working.
(d) A classmate connects a diode directly across a 9 V battery in forward bias without a resistor. Predict what will happen and explain why a current-limiting resistor is essential.
(e) In Indian homes, diode rectifiers are used in mobile chargers and power supplies. Explain why understanding forward and reverse bias is essential for designing these everyday devices.