Electrostatics Question 409
Question: Two positive point charges of $ 12\mu C $ and $ 8\mu C $ are 10cm apart. The work done in bringing them 4 cm closer is [AMU 2000]
Options:
A) 5.8 J
B) 5.8 eV
C) 13 J
D) 13 eV
Show Answer
Answer:
Correct Answer: C
Solution:
$ W=U _{f}-U _{i}=9\times 10^{9}\times Q _{1}Q _{2}[ \frac{1}{r _{2}}-\frac{1}{r _{1}} ] $
therefore $ W=9\times 10^{9}\times 12\times {{10}^{-6}}\times 8\times {{10}^{-6}}[ \frac{1}{4\times 10{{}^{-2}}}-\frac{1}{10\times 10{{}^{-2}}} ] $ = 12.96 J » 13 J
