# Electronic Devices and Circuits Questions and Answers – Diffusion

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

1. What is the SI unit of electron diffusion constant?
a) cm2/s
b) m2/s
c) m/s
d) none

Explanation: J=eDdn/dx
So D=q*m/ (q*s*(1/m))
=m2/s.

2. Calculate the diffusion current density when the concentration of electron varies from the 1*1018 to 7*1017 cm-3 over a distance of 0.10 cm.D=225cm2/s
a) 100 A/cm2
b) 108 A/cm2
c) 0.01A/cm2
d) None

Explanation: J=eDdn/dx
J=1.6*10-19*225*(1018-(7*1017))/0.1
=108A/cm2.

3. Which is the correct formula for the Jp?
a) Jp=qDdp/dx
b) Jp=pDdn/dx
c) Jp=-qDdp/dx
d) None

Explanation: Jp is negative for the p type of semiconductors.

4. What is the direction of the electron diffusion current density relative to the electron flux?
a) Same direction
b) Opposite to each other
c) Perpendicular to each other
d) At 270 degrees to each other

Explanation: From the graph between electron concentration and the distance, we can see that the direction of the electron diffusion current density is opposite to the electron flux.

5. In diffusion, the particles flow from a region of _______ to region of ___________
a) High, low
b) Low , high
c) High , medium
d) Low, medium

Explanation: Diffusion is the process of flow of particles form the region of the high concentration to a region of low concentration.

6. Which of the following parameter describes the best movement of the electrons inside a semiconductor?
b) Diffusion
c) Mobility

Explanation: Mobility is defined as the movement of the electrons inside a semiconductor. On the other hand, velocity gradient is the ratio of velocity to distance.

7. Which of the following term isn’t a part of the total current density in a semiconductor?
a) Temperature
b) µ
c) e
d) E

Explanation: J=enµE+epµE+eDdn/dx-eDdp/dx
So, temperature isn’t a part of the equation.

8. What does dn/dx represent?
d) None

9. Calculate the diffusion constant for the holes when the mobility of the holes is 400cm2/V-s and temperature is 300K?
a) 1.035m m2/s
b) 0.035m m2/s
c) 1.5m m2/s
d) 1.9m m2/s

Explanation: Dp=VT*μn
= (1.38*10-23*300*400*10-2)/ (1.6*10-19)
= 1.035m m2/s.

10. Calculate the diffusion constant for the electrons when the mobility of the electrons is 325cm2/V-s and temperature is 300K?
a) 0.85 m2/s
b) 0.084 m2/s
c) 0.58 m2/s
d) 0.95 m2/s

Explanation: Dn=VT*μn
= (1.38*10-23*300*325*10-2)/ (1.6*10-19)
= 0.084 m2/s.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

To practice all areas of Electronic Devices and Circuits, here is complete set of 1000+ Multiple Choice Questions and Answers. 