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Question
Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is 8.0 × 103 N m2/C.
- What is the net charge inside the box?
- If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? Why or Why not?
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Solution
(a) Φ = 8 × 103 N m2 C−1
`q/ε_0 = 8 xx 10^3` N m2 C−1
∴ q = 8 × 103 ε0
= 8 × 103 × 8.85 × 10−12
= 7.08 × 10−8 C
(b) As Φ = 0
`q_"net"/ε_0 = 0`
∴ `q_"net" = 0`
Even though a closed surface may have internal charges, the net charge it contains is zero.
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