Two point charges +10 μC and −10 μC are placed at a distance of 20 mm apart. The resultant electric field at a point on their axial line 10 cm away from the +10 μC charge on its own side is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2.75 x 106 NC−1
On the axial line the fields of the two charges point in opposite directions, and the nearer charge (+10 μC) gives the larger field. The point is 10 cm from +10 μC and 10 cm + 2 cm = 12 cm from −10 μC.
\( \displaystyle E_{+} = \frac{9\times10^{9} \times 10\times10^{-6}}{(0.10)^{2}} = 9\times10^{6}\,\mathrm{N\,C^{-1}} \)
\( \displaystyle E_{-} = \frac{9\times10^{9} \times 10\times10^{-6}}{(0.12)^{2}} = 6.25\times10^{6}\,\mathrm{N\,C^{-1}} \)
\( \displaystyle E = E_{+} - E_{-} = 2.75\times10^{6}\,\mathrm{N\,C^{-1}} \)
The resultant field points along the axis, away from the +10 μC charge.
Note: NTA picked this question from an NCERT (2026-27) example and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Physical Significance of Dipoles – …
