Question

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

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

Answer 1

Answer: (B)

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