Question

A current flows in a wire of circular cross-section with the free electrons travelling with a mean drift velocity v. If an equal current flows in a wire of twice the radius, then the new mean drift velocity is

• A. v
• B. $\frac{v}{2}$
• C. $\frac{v}{4}$
• D. None of these

Answer 1

The correct option is C $\frac{v}{4}$

By using $v_d=\frac{i}{neA}\Rightarrow v_d\alpha \frac{1}{A}\Rightarrow v^{{}^{\prime }}=\frac{v}{4}$