The resistivity of a metal is $1 \times 10^{-8} \Omega \cdot m$. If it contains $9 \times 10^{28}$ electrons per $m^3$, then the relaxation time of electrons inside the metal is nearly (electron mass $= 9 \times 10^{-31} \ kg$).

  • A
    $4 \times 10^{-14} \ s$
  • B
    $7 \times 10^{-14} \ s$
  • C
    $1.0 \times 10^{-14} \ s$
  • D
    $9 \times 10^{-14} \ s$

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Assume a hypothetical wire in which free electron density changes with temperature in proportionality $n \propto T$,assuming $\tau$ (relaxation time of collision) and dimensions of the wire remain unchanged with increasing temperature. Which one of the resistance $v/s$ temperature graphs is true?

Choose the correct option with respect to the statements $A$ and $B$:
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$(B)$: When an electric field is applied across a conductor,the drift velocity of electrons is independent of time.

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There is a current of $1.344 \, A$ in a copper wire whose area of cross-section normal to the length of the wire is $1 \, mm^2$. If the number of free electrons per $cm^3$ is $8.4 \times 10^{22}$, then the drift velocity would be

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