A cube of side 5 cm has a charge of 6 C. The surface density of charge is_________?
Correct answer: D. 400 C m-2
- A. 100 C m-2
- B. 200 C m-2
- C. 300 C m-2
- D. 400 C m-2
Explanation
The cube side is 5 cm = 0.05 m, and its total surface area is 6a² = 6(0.05 m)² = 0.015 m². Surface charge density is σ = Q/A = 6 C ÷ 0.015 m² = 400 C m^-2. The likely choice is b, because students may use only one face area, a² = 0.0025 m², instead of the complete surface area of the cube.
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An electric field is the force experienced per unit positive test charge, with the field of a point charge given by E = kQ/r² and directed away from positive charges or toward negative charges. Questions involve field lines, superposition and force on a charge, while electric field must be distinguished from electric potential.
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