COMEDK2020PhysicsElectrostatics
Two point charges A=+3 nC and B=+1 nC are placed 5 ~cm apart in air. The work done to move charge B towards A by 1 ~cm is
Options
- A20 10⁻⁷ ~J
- B1.35 10⁻⁷ ~J
- C27 10⁻⁷ ~J
- D121 10⁻⁷ ~J
Correct answer
B. 1.35 10⁻⁷ ~J
Step-by-step solution
The given situation is shown below aligned r₁ &=1 ~cm &=1 10⁻² ~m r₂ &=5-1 &=4 ~cm &=4 10⁻² ~m aligned Required work done = Changes in potential energy aligned &=k q_ A q_ B [ 1 r₂ - 1 r₁ ] &=9 10⁹ 3 10⁻⁹ 10⁻⁹ & [ 1 4 10⁻² - 1 1 10⁻² ] &=1.35 10⁻⁷ ~J aligned