Question

An electron is placed on $ X $ -axis where the electric potential depends on $ x $ as shown in figures (the potential does not depend on $ y $ and $ z $ ). What is the electric force on the electron ?

• A. $ 4.0 \times 10^{-18} \, N $
• B. $ 8.0 \times 10^{-18} \, N $
• C. $ 3.2 \times 10^{-16} \, N $
• D. $ 4.0 \times 10^{-16} \, N $

Answer 1

Answer: (D)

From the graph, given in the question
The slope of the electric potential versus distance graph
$\frac{dv}{dx}=\frac{-500}{20\times 10^{-2}} V/m$
$=-2.5\times 10^{3} V/m$
Since, we know that
Electric field, $E=-\frac{dv}{dx}$ (at a point)
$E=2.5\times 10^{3} V/m$
$\therefore $ The electric force on the electron at that point
$F=eE$
$=1.6\times10^{-19}\times25\times10^{3}$
$=4\times 10^{-16}\,N$