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Electric Conductivity - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main
Quick Facts
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Electric Conductivity is considered one the most difficult concept.
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21 Questions around this concept.
Solve by difficulty
The effect of the increase in temperature on the number of electrons in the conduction band and resistance of a semiconductor will be as:
Copper has face centered cubic (fcc) lattice with interatomic spacing equal to. The value of lattice constant for this lattice is
A potential difference of 2V is applied between the opposite faces of a Ge crystal plate of area and thickness 0.5 mm. If the concentration of electrons in Ge is
and mobilities of electrons and holes are
respectively, then the current flowing through the plate will be
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The resistivity of pure silicon is and the mobilities of electrons and holes in it are 0.135 and
-s respectively. The resistivity of a specimen of silicon doped with
atoms of phosphorus per meter is:
When plate voltage in the diode valve is increased from to
then plate current increases from
to
. The dynamic plate resistance will be
The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm, is incident on it. The band gap in (eV) for the semiconductor is
For a given plate-voltage, the plate current in a triode is maximum when the potential of
A metallic surface with a work function of, on heating to a temperature of gives an emission current of
If another metallic surface having the same surface area, same emission constant but work function
is heated to a temperature of, then the emission current will be
A potential difference of is applied between the opposite faces of a Ge crystal plate of area
and thickness
. If the concentration of electrons in G eis
and mobilities of electrons and holes are
respectively, then the current flowing through the plate will be
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Download EBookThe current in a triode at anode potential and grid potential
is
. If grid potential is changed to
, the current becomes
the value of trans conductance
will be
Concepts Covered - 1
Electric Conductivity
Electrical Conductivity (σ)-
The semiconductor conducts electricity with the help of these two types of electricity or charge carriers (i.e electrons and holes).
These holes and electrons move in the opposite direction. The electrons always tend to move in opposite direction to the applied electric field.
Let the mobility of the hole in the crystal is μh and the mobility of electron in the same crystal is μe
The current density due to drift of holes is given by,
$
J_h=e n_h v_h=e n_h \mu_h E
$
And The current density due to the drift of electrons is given by,
$
J_e=\mathrm{en}_{\mathrm{e}} \mathrm{v}_e=\mathrm{en}_{\mathrm{e}} \mu_e E
$
hence resultant current density would be
$
\begin{aligned}
& J=J_h+J_e=e n_h v_h+e n_e v_e=e n_h \mu_h E+e n_e \mu_e E=\left(n_h \mu_h+n_e \mu_e\right) e E \\
& \text { and } J=\sigma E
\end{aligned}
$
So, the general equation for conductivity is given as
$
\sigma=e\left(n_e \mu_e+n_h \mu_h\right)
$
where
$n_e=$ electron density
$n_h=$ hole density
$\mu_e=$ mobility of electron
$\mu_h=$ mobility of holes
For intrinsic semiconductors (no impurities)-
As the number of electrons will be equal to the number of holes.
i.e $n_e=n_h=n_i$
$
\sigma=n_i e\left(\mu_e+\mu_h\right)
$
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