Answer: Because of the different wave speed from light and sound. Explanation: There is a major difference between the speed wave of light and sound, light travels at 186, 282 miles per second, and sound can travel at different speeds and its significantly slower so it is easier to measure it
Explanation:
We have that the electric field at the center of the metal ball due only to the charges on the surface of the metal ball is

From the question we are told that
A solid metal ball of radius 1.5 cm
bearing a charge of -15 nC is located near a hollow plastic ball of radius 1.9 cm bearing
uniformly distributed charge of -7 nC
The distance between the centers of the balls is 9 cm
Generally the equation for the electric field is mathematically given as


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