# Electronic Devices and Circuits Questions and Answers – Conductivity of a Semiconductor

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

1. What is the SI unit of conductivity?
a) Ωm
b) (Ωm)-1
c) Ω
d) m

Explanation: The formula of the conductivity is the σ=1/ρ.
So, the unit of resistivity is Ωm.
Now, the unit of conductivity becomes the inverse of resistivity.

2. Which of the following expressions doesn’t represent the correct formula for Drift current density?
a) J=σE
b) J=qnµE
c) J=µE
d) None

Explanation: The following formulae represent the correct expression for drift current density,
J=σE
And J=qnµE.

3. Does a semiconductor satisfy the ohm’s law?
a) True
b) False

Explanation: V=IR
J=σE
I/A=σ(V/L)
V=(L/ σA)*I=(ρL)*I/A=IR
Thus, above equation satisfies Ohm’s law.

4. In which range of temperature, freeze out point begins to occur?
a) Higher range
b) Lower range
c) Middle range
d) None

Explanation: At lower range of temperature, the concentration and conductivity decreases with lowering of the temperature.

5. Which of the following expression represents the correct formula for the conductivity in an intrinsic material?
a) ρ=e(μn+μp )ni
b) σ=e(μn+μp )ni
c) σ=1/(e(μn+μp )ni)
d) ρ=1/(e(μn+μp )ni)

Explanation: Option b is the correct formula.

6. What is the voltage difference if the current is 1mA and length and area is 2cm and 4cm2 respectively?(ρ=2Ωm)
a) 0.025V
b) 25V
c) 0.25V
d) None

Explanation: V=IR
R=ρl/(A)=2*2/4=100Ω
V=1mA*100
=0.1V.

7. Is resistivity is a function of temperature?
a)True
b)False

Explanation: Resistance depends on the temperature and the resistivity depends on the resistance, so now the resistivity depends on the temperature.

8. What is the electric field when the voltage applied is 5V and the length is 100cm?
a) 0.5V/m
b) 5V/m
c) 50V/m
d) None

Explanation: E=V/L=5/100cm=5V/m.

9. Calculate the average random thermal energy at T=300K?
a) 0.038eV
b) 3.8eV
c) 38eV
d) 0.38eV

Explanation: Average random thermal energy=3/2*k*T=0.038eV.

10. In the below figure, a semiconductor having an area ‘A’ and length ‘L’ and carrying current ‘I’ applied a voltage of ‘V’ volts across it. Calculate the relation between V and A?

a) V = ((ρ*L)/A)*I
b) V = ((ρ*A)/L)*I
c) V = ((ρ*I)/(A*L))
d) V = ((ρ*I*A*L)

Explanation: Option A, satisfies the Ohm’s law which is V=IR where R=(ρl)/A.

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

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