Electric charges were imparted to the metal ball. How can one experimentally prove that charges are located on its surface?

Let’s carry out an experiment with a hollow metal conductor ball on an insulating support. With a test ball on the insulating handle, we touch the outer surface of the charged conductor, and then the electrometer. The electrometer needle has deviated from its original position. Consequently, there are charges on the outer surface of the ball. We repeat the experiment by touching the test ball to the inner surface of the conductor. Let’s touch the rod of the electrometer again with the test ball. In this case, the arrow of the device does not deviate. The trial ball has not acquired any charge from the charged hollow ball. Therefore, there is no electric charge inside the metal conductor, which means there is no field either. The charges on the conductor are located only on its surface.

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