Engineering Questions with Answers - Multiple Choice Questions

# MCQs on Conductivity of a Semiconductor

1 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question

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 - Question In the above 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)