Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Electrostatics question

2025 · 23 Jan · Shift 2 · Q64
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Physics
  4. /Electrostatics
  5. /2025 · 23 Jan · Shift 2 · Q64

Electrostatics question

2025 · 23 Jan · Shift 2 · Q64

JEE MainPhysicsElectrostaticsMCQ+4 / −1
Two charges 7μc7 \mu \mathrm{c}7μc and −4μc-4 \mu \mathrm{c}−4μc are placed at (−7 cm,0,0)(-7 \mathrm{~cm}, 0,0)(−7 cm,0,0) and (7 cm,0,0)(7 \mathrm{~cm}, 0,0)(7 cm,0,0) respectively. Given, ϵ0=8.85×10−12C2 N−1 m−2\epsilon_0=8.85 \times 10^{-12} \mathrm{C}^2 \mathrm{~N}^{-1} \mathrm{~m}^{-2}ϵ0​=8.85×10−12C2 N−1 m−2, the electrostatic potential energy of the charge configuration is :
  1. A
    −2.0-2.0−2.0 J
  2. B
    −1.5-1.5−1.5 J
  3. C
    −1.2-1.2−1.2 J
  4. D
    −1.8-1.8−1.8 J
View written solutionFree

Correct answer: D

  1. Use the formula for electrostatic potential energy

For two point charges separated by distance rrr,

U=14πε0q1q2rU=\frac{1}{4\pi\varepsilon_0}\frac{q_1 q_2}{r}U=4πε0​1​rq1​q2​​

  1. Write the given data
  • q1=7 μC=7×10−6 Cq_1=7\,\mu C=7\times 10^{-6}\,Cq1​=7μC=7×10−6C
  • q2=−4 μC=−4×10−6 Cq_2=-4\,\mu C=-4\times 10^{-6}\,Cq2​=−4μC=−4×10−6C
  • Positions are (−7 cm,0,0)(-7\,\text{cm},0,0)(−7cm,0,0) and (7 cm,0,0)(7\,\text{cm},0,0)(7cm,0,0)

So the separation is

r=14 cm=0.14 mr=14\,\text{cm}=0.14\,\text{m}r=14cm=0.14m

Also,

14πε0=14π(8.85×10−12)≈9×109 N m2/C2\frac{1}{4\pi\varepsilon_0}=\frac{1}{4\pi(8.85\times 10^{-12})}\approx 9\times 10^9\,\text{N m}^2/\text{C}^24πε0​1​=4π(8.85×10−12)1​≈9×109N m2/C2

  1. Substitute into the formula

U=9×109⋅(7×10−6)(−4×10−6)0.14U=9\times 10^9\cdot \frac{(7\times 10^{-6})(-4\times 10^{-6})}{0.14}U=9×109⋅0.14(7×10−6)(−4×10−6)​

First compute the product of charges:

(7×10−6)(−4×10−6)=−28×10−12(7\times 10^{-6})(-4\times 10^{-6})=-28\times 10^{-12}(7×10−6)(−4×10−6)=−28×10−12

So,

U=9×109⋅−28×10−120.14U=9\times 10^9\cdot \frac{-28\times 10^{-12}}{0.14}U=9×109⋅0.14−28×10−12​

U=9×109⋅(−2×10−10)U=9\times 10^9\cdot (-2\times 10^{-10})U=9×109⋅(−2×10−10)

U=−1.8 JU=-1.8\,\text{J}U=−1.8J

  1. Match with the options

Thus the electrostatic potential energy is

−1.8 J\boxed{-1.8\,\text{J}}−1.8J​

So the correct option is D.

PreviousNext

More from Electrostatics

  • Consider a parallel plate capacitor of area A (of each plate) and separation ' d' between the plates. If E is the electric field and ε0​ is the permittivity of free space between the plates, then potential energy stored in…2025 · MCQ
  • A square loop of sides a=1 m is held normally in front of a point charge q=1C at a distance 2a​. The flux of the electric field through the shaded region is p5​×ε0​1​CNm2​… Includes diagram2025 · Numerical
  • A small uncharged conducting sphere is placed in contact with an identical sphere but having 4×10−8C charge and then removed to a distance such that the force of repulsion between them is $9 \times 10^{-3}…2025 · MCQ
  • In the first configuration (1) as shown in the figure, four identical charges (q0​) are kept at the corners A, B, C and D of square of side length 'a'. In the second configuration (2), the same charges are shifted to mid… Includes diagram2025 · MCQ
  • Three infinitely long wires with linear charge density λ are placed along the x−axis,y−axis and z− axis respectively. Which of the following denotes an equipotential surface?2025 · MCQ
  • A particle of mass ' m' and charge 'q' is fastened to one end 'A' of a massless string having equilibrium length l, whose other end is fixed at point ' O'. The whole system is placed on a frictionless horizontal plane and is… Includes diagram2025 · MCQ
  • An electric dipole of dipole moment 6×10−6Cm is placed in uniform electric field of magnitude 106V/m. Initially, the dipole moment is parallel to electric field. The work that needs to be…2025 · Numerical
  • An electric dipole of mass m, charge q, and length l is placed in a uniform electric field E=E0​i^. When the dipole is rotated slightly from its equilibrium position and released, the time period of its oscillations…2025 · MCQ