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PHY 102 Test Compilation PHY 102 10 Objective Question

Question

The electric field everywhere on the surface of a hollow sphere of radius 6cm is measured to be 2.9 x 104 N/C. what is the charge enclosed by the surface?
Options
A 5.1 µC
B 0.051 µC
C 0.012 µC
Correct Answer
D 1.3 µC
Correct Answer

Option C is the correct answer.

Detailed Explanation

Given:Electric field (E) on the surface = 2.9 x 104 N/CRadius of the sphere (R) = 6 cm = 0.06 mAccording to Gauss's Law, for a spherically symmetric charge distribution or a hollow sphere with charge enclosed, the electric field outside (or on the surface) is given by:E = kQ / R2Where k = 1 / (4πε₀) = 9 x 109 Nm2/C2.We need to find the enclosed charge (Q):Q = E * R2 / kQ = (2.9 x 104 N/C) * (0.06 m)2 / (9 x 109 Nm2/C2)Q = (2.9 x 104) * (0.0036) / (9 x 109)Q = (0.1044 x 104) / (9 x 109)Q = 1044 / (9 x 109) = 116 x 10-9 C = 0.116 x 10-6 C = 0.116 µC.Let's re-examine the options: 0.012 µC is significantly different. Let's re-calculate using 0.012µC to see if it matches the given E. If Q = 0.012 µC = 0.012 x 10-6 C.E = (9 x 109) * (0.012 x 10-6) / (0.06)2E = (0.108 x 103) / 0.0036 = 108 / 0.0036 = 30000 N/C = 3.0 x 104 N/C.This value (3.0 x 104 N/C) is very close to the given electric field (2.9 x 104 N/C). The discrepancy likely arises from rounding in the question's values or options.Therefore, 0.012 µC is the closest and most probable answer.

Hint

Use Gauss's Law or the formula for the electric field of a point charge (E = kQ/R2) to relate the electric field, charge, and radius. Remember to convert units to SI (cm to m) and that k = 9 x 109 Nm2/C2.

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