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Electric Conductivity - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

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  • Electric Conductivity is considered one the most difficult concept.

  • 21 Questions around this concept.

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The effect of the increase in temperature on the number of electrons in the conduction band \mathrm{(n_{e})} and resistance of a semiconductor will be as:

Copper has face centered cubic (fcc) lattice with interatomic spacing equal to\mathrm{2.54 \AA }. 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 \mathrm{1 cm^{2}} and thickness 0.5 mm. If the concentration of electrons in Ge is \mathrm{2 \times 10^{19} / \mathrm{m}^3} and mobilities of electrons and holes are  \mathrm{0.36\frac{\mathrm{m}^2}{\text { volt }-\mathrm{sec}} \text { and } 0.14 \frac{\mathrm{m}^2}{\text { volt }-\mathrm{sec}}} respectively, then the current flowing through the plate will be

 

The resistivity of pure silicon is \mathrm{2300 \Omega-m} and the mobilities of electrons and holes in it are 0.135 and \mathrm{0.048 \mathrm{~m}^{2} / \mathrm{V}}-s respectively. The resistivity of a specimen of silicon doped with \mathrm{10^{19}} atoms of phosphorus per meter is:  

When plate voltage in the diode valve is increased from\mathrm{100 volt} to \mathrm{150 volt} then plate current increases from7.5 \mathrm{~mA} to 12 \mathrm{~mA}. 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

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A metallic surface with a work function of, on heating to a temperature of 800 \mathrm{~K} gives an emission current of 1 \mathrm{~mA}. If another metallic surface having the same surface area, same emission constant but work function  4 \mathrm{eV} is heated to a temperature of, then the emission current will be

A potential difference of 2 \mathrm{~V} is applied between the opposite faces of a Ge crystal plate of area 1 \mathrm{~cm}^2 and thickness0.5 \mathrm{~mm}. If the concentration of electrons in G eis  2 \times 10^{19} / \mathrm{m}^3 and mobilities of electrons and holes are0.36 \frac{\mathrm{m}^2}{\text { volt-s }}\, \, and\,\, 0.14 \frac{\mathrm{m}^2}{\text { volt-s }} respectively, then the current flowing through the plate will be

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The current in a triode at anode potential 100 \mathrm{~V} and grid potential -1.2 \mathrm{~V} is 7.5 \mathrm{~mA}. If grid potential is changed to -2.2 \mathrm{~V}, the current becomes 5.5 \mathrm{~mA}. the value of trans conductance \left(g_m\right) 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}=en_h v_{h}=e n_h \mu_{h} E

And The current density due to the drift of electrons is given by,

J_{e}=\operatorname{en_ev}_{e}=\operatorname{en_e} \mu_{e} E

hence resultant current density would be

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 \\ and \ \ \ J =\sigma E

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 (\mu _{e}+ \mu _{h} )

 

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Electric Conductivity

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