# Diode Capacitances MCQ’s

This set of Electronic Devices & Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Diode Capacitances”.

1. If C_{T} is the transition capacitance, which of the following are true?

1) in forward bias, C_{T} dominates

2) in reverse bias, C_{T} dominates

3) in forward bias, diffusion capacitance dominates

4) in reverse bias, diffusion capacitance dominates

a) 1 only

b) 2only

c) 2 and 3

d) 3 only

2. For an abrupt PN junction diode, small signal capacitance is 1nF/cm^{2} at zero bias condition.If the built in voltage, V_{bi} is 1V, the capacitance at reverse bias of 99V is?

a) 0.1nF/cm^{2}

b) 1nF/cm^{2}

c) 1.5nF/cm^{2}

d) 2nF/cm^{2}

3. Compared to a PN junction with N_{A}=10^{14}/CM^{3}, which one of the following is true for N_{A}=N_{D}= 10^{20}/CM^{3}?

a) depletion capacitance decreases

b) depletion capacitance increases

c) depletion capacitance remains same

d) depletion capacitance can’t be predicted

4. The built in capacitance V_{0} for a step graded PN junction is 0.75V. Junction capacitance C_{j} at reverse bias when V_{R}=1.25V is 5pF. The value of C_{j} when V_{R}=7.25V is?

a) 0.1pF

b) 1.7pF

c) 1pF

d) 2.5Pf

5. A silicon PN junction diode under revers bias has depletion width of 10µm, relative permittivity is 11.7 and permittivity, ε0 =8.85×10^{-12}F/m. Then depletion capacitance /m^{2} =?

a) 0.1µF/m^{2}

b) 1.7µF/m^{2}

c) 10µF/m^{2}

d) 0.5µF/m^{2}

6. The C_{T} for an abrupt PN junction diode is ________

a) C_{T} = K/(V_{0}+V_{B})^{1/2}

b) C_{T} = K/(V_{0}+V_{B})^{-1/2}

c) C_{T} = K/(V_{0}+V_{B})^{1/3}

d) C_{T} = K/(V_{0}+V_{B})^{-1/3}

7. Consider an abrupt PN junction. Let V0 be the built in potential of this junction and VR be the reverse bias voltage applied. If the junction capacitance C_{j} is 1pF for V_{0}+V_{R} =1V, then for V_{0}+V_{R} =4V what will be the value of C_{j}?

a) 0.1pF

b) 1.7pF

c) 1pF

d) 0.5Pf

8. The transition capacitance, C_{T} of a PN junction having uniform doping in both sides, varies with junction voltage as ________

a) (VB )^{1/2}

b) (VB )^{-1/2}

c) (VB )^{1/4}

d) (VB )^{-1/4}

9. The diffusion capacitance of a PN junction _______

a) decreases with increasing current and increasing temperature

b) decreases with decreasing current and increasing temperature

c) increasing with increasing current and increasing temperature

d) doesnot depend on current and temperature

10. Transition capacitance is also called as _______

a) diffusion capacitance

b) depletion capacitance

c) conductance capacitance

d) resistive capacitance