Question

An electron in potentiometer with experiences a force $2.4\times {10}^{-19}N$. The length of potentiometer wire is $6m$. The emf of the battery connected across the wire is (electronic charge $=1.6\times {10}^{-19}C$)

• A. $6V$
• B. $9V$
• C. $12V$
• D. $15V$

Answer 1

The correct option is B $9V$

Force experienced by electron $F=qE$ where $E=$ Electric field intensity
$\therefore 2.4\times {10}^{-19}=1.6\times {10}^{-19}E\Rightarrow E=1.5N/m$
Moreover $E=$ potential gradient
$E=\frac{dV}{dl}$
$\therefore E\times l=V\Rightarrow V=1.5\times 6=9V$