Question

Two point charges $+ 10^{-7} C$ and $- 10^{-7} C$ are placed at $A$ and $B, 20 \,cm$ apart as shown in the figure. Calculate the electric field at $C, \,20\, cm$ apart form both $A$ and $B$ .

• A. $1.5 \times 10^{-5} N/C$
• B. $2.2 \times 10^{4} N/C$
• C. $3.5 \times 10^{6} N/C$
• D. $3.0 \times 10^{5} N/C$

Answer 1

Answer: (B)

$2.2 \times 10^{4} N/C$

Answer 2

The magnitude of each electric field vector at point $C$ due to charge $q_1$ and $q_2$
$E = \frac{1}{4\pi \varepsilon_0} \cdot \frac{q}{r^2}$
$E = \frac{9 \times 10^9 \times 10^{-7}}{(20 \times 10^{-2})^2}$
$= 2.2 \times 10^4 \,N/C$