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Q51 (NDA-II/2010) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Electricity and magnetism Answer Verified

If two conducting spheres are separately charged and then brought in contact

Result
Your answer: —  Â·  Correct: B
Explanation

When two conducting spheres are brought into contact, charge redistribution occurs until they reach a common electric potential [t2][t3]. According to the law of conservation of charge, the total charge of the isolated system remains constant throughout this process [t7]. However, the total electrostatic energy is generally not conserved. The initial energy of the system is given by the sum of individual energies (W = 1/2 QV) [t4]. Upon contact, charges flow between the spheres due to the potential difference [c2]. This movement of charge encounters resistance and involves work, leading to energy dissipation in the form of heat or electromagnetic radiation [c5][t1]. Consequently, while the total charge is conserved, the total energy of the system decreases. The final potential is a weighted average based on capacitance (radii), not necessarily a simple arithmetic mean [t3][t6].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE > p. 173
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > Figure 11.3 > p. 176
  3. [3] https://ncert.nic.in/textbook/pdf/leph102.pdf
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