JEE Main 2026 — Jan 28, Shift 1 — Physics solution

JEE Main2026Jan 28, Shift 1Physics

Two point charges of 1 nC and 2 nC are placed at the two corners of equilateral triangle of side 3 cm. The work done in bringing a charge of 3 nC from infinity to the third corner of the triangle is _____ $μ$ J. ( $\frac{1}{4 π ϵ _{0}} = 9 \times 1 0^{9}$ N·m $^{2}$ /C $^{2}$ )

A
2.7
B
5.4
C
3.3
D
27

Solution

Work to bring $q_{3} = 3$ nC from infinity to the third corner equals $q_{3}$ times the potential at that corner due to $q_{1} = 1$ nC and $q_{2} = 2$ nC, each at distance $ℓ = 3$ cm:

$W = \frac{k q _{3}}{ℓ} (q_{1} + q_{2}) = \frac{9 \times 1 0 ^{9} \times 3 \times 1 0 ^{- 9}}{0.03} (1 + 2) \times 1 0^{- 9}$

$= \frac{9 \times 1 0 ^{9}}{0.03} \cdot 3 \times 1 0^{- 9} \cdot 3 \times 1 0^{- 9}$

$= 3 \times 1 0^{11} \cdot 9 \times 1 0^{- 18} = 27 \times 1 0^{- 7}$ J $= 2.7 μ$ J.

Option (1).

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