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A steady current $I$ flows through a wire of radius $r$, length $L$ and resistivity $\rho$. The current produces heat in the wire. The rate of heat loss in a wire is proportional to its surface area. The steady temperature of the wire is independent of
If the resistance of a conductor is $5\,\Omega\,\,$ at $\,50\,^oC$ and $7\, \Omega\,$ at $\,100\,^oC$ then the mean temperature coefficient of resistance of the material is ............... $^oC$
$n$ identical cells are joined in series with two cells $A$ and $B$ with reversed polarities. $emf$ of each cell is $E$ and internal resistance is $r$. Potential difference across cell $A$ and $B$ is : $(n > 4)$
A Daniel cell is balanced on $125\,cm$ length of a potentiometer wire. Now the cell is short-circuited by a resistance $2\, ohm$ and the balance is obtained at $100\,cm$. The internal resistance of the Daniel cell is .............. $ohm$
The heat generated through $2 \,ohm$ and $8\, ohm$ resistances separately, when a condenser of $200\,\mu F$ capacity charged to $200\, V$ is discharged one by one, will be
What is the number density of donor atoms which must be added to a pure germanium semiconductor to make $n-$ type semiconductor of conductivity $6.4\ {\Omega ^{ - 1}}\,c{m^{ - 1}}$? The mobility of electr ons in $n-$ type germanium is $4 \times {10^3}\ cm^2\ V^{-1}\ s^{-1}$. Neglect the contribution of holes to conductivity
A cylindrical metal wire of length $l$ and cross sections area $S$, has resistance $R$, conductance $G$, conductivity $\sigma$ and resistivity $\rho$. Which one of the following expressions for $\sigma$ is valid