# The Continuity Equation MCQ’s

This set of Electronic Devices & Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Continuity Equation”.

1. Which of the following is the Taylor’s expression?
a)

b)

c)

d)

2. Calculate the number of coulombs per second if the area is 4cm2, recombination rate of hole is 1000 cm-3/s and the differential length is 2mm.
a) 1.28*10-23
b) 1.28*10-22
c) 1.28*10-21
d) 1.28*10-20

3. What does p/τ represent?
a) holes
b) time
c) holes per second lost
d) p per unit time

4. The current entering the volume at x is I and leaving is I+Δi , the number of coulombs per second will be equal to δI. Is it true or false?
a) True
b) False

5. What of the following conditions satisfies when the number of holes which are thermally generated is equal to the holes lost by recombination?
a) I≠0
b) dp/dt≠0
c) g=p/τ
d) g≠p/τ

6. Which of the following represents the continuity equation?
a) dp/dt=-(p-p0)/τp+Dp(d2p/dx2)-µpd(ρϵ)/dx
b) dp/dt=-(p-p0)/τp-Dp(d2p/dx2)-µpd(ρϵ)/dx
c) dp/dt=-(p-p0)/τp+Dp(d2p/dx2)+µpd(ρϵ)/dx
d) dp/dt=(p-p0)/τp-Dp(d2p/dx2)-µpd(ρϵ)/dx

7. The change in the carrier density is due to
a) Flow of incoming flux
b) Flow of outgoing flux
c) Difference of flow between incoming and outgoing flux
d) Difference of flow between incoming and outgoing flux plus generation and minus recombination

8. What is the diffusion length for holes when Dp=25cm2/s and τp=25s?
a) 25cm
b) 1cm
c) 0.04cm
d) 50cm

9. What is the diffusion length for electrons when Dn=10cm2/s and τn=40s?
a) 50cm
b) 25cm
c) 20cm
d) 15cm

10. Which of the following represents the best definition for the diffusion length for holes?
a) Average distance which an electron is injected travels before recombining with an electron
b) Average distance which a hole is injected travels before recombining with an electron
c) Average distance which a hole is injected travels before recombining with a hole
d) Average distance which an electron is injected before recombining with a hole

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