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InterviewSolution
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If the earth’s surface is treated as a conducting surface with some charge, what should be the order of magnitude of the charge per unit area, in C/m2, so that a proton remains suspended in space near the earth’s surface? (a) 10-18 (b) 10-12 (c) 10-6 (d) 1 |
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Answer» Correct Answer is: (a) 10-18 Let σ = charge per unit area on the earth’s surface. Then, the field near the surface = E = σ/ε0. The upward force on a proton = eE = eσ/ε0. The downward force = mg.. For equilibrium, mg = eσ/ε0 or σ = ε0mg/ε0. σ = 8.85 x 10-12 x 1.67 x 10-27 x 10 / 1.6 x 10-19 C/m2 ~ 10-18 C/m2. |
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