Q4 / 250 · NTA Abhyas (NEET) 2020 · Physics · Electrostatics

Two point charges A=+3 nC and B=+1 nC are placed 5 cm apart in the air. The work done to move charge B towards A by 1 cm is

  • A
    2.0×10-7 J
  • B
    2.7×10-7J
  • C
    12.1×10-7J
  • Correct answer
    D
    1.35×10-7 J

Solution

Given,

A=+ 3 nC=3×10-9 C

B=+ 1 nC=1×10-9 C

Distance, r1=5 cm=0.05 m=5×10-2 m

Work done W=UB-UA

=kq1q2r2-kq1q2r1

Here, r2=r1-1

r2=5-1=4 cm=0.04 m=4×10-2 m

=kq1q21r2-1r1

=9×109×3×10-9×1×10-9

14×10-2-15×10-2

=27×10-9×15×4×10-2

=2720×10-7

=1.35×10-7J

Hence, the correct answer is option: 'D'.

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