A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A)
B) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A)
C) Assertion (A) is true but Reason (R) is false
D) Assertion (A) is false and Reason (R) is also false
Correct Answer: A
Solution :
(a) Drift velocity of free electrons is given by, \[{{v}_{d}}=\frac{eE}{m}\tau \] \[\text{where,}\,\text{E=}\frac{\text{Potential}\,\,\text{difference}}{\text{length}}\text{=}\frac{\text{V}}{\text{l}}\] \[\therefore {{\text{v}}_{d}}=\frac{eV}{ml}\tau \] i.e., \[{{\text{v}}_{d}}\propto =\frac{1}{l}\] where, \[\frac{eV\tau }{m}\] is constant. It mean if (is doubled, the drift velocity will become half of the original value.
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