Question

A neutral electroscope is shown in the figure. If a positively charged metal rod is brought near the knob of the electroscope, identify the true statement?

• A. The electroscope can be charged negatively without the positively charged rod touching the knob and using only a grounding wire
• B. The electroscope can be charged positively without the positively charged rod touching the knob and using only a grounding wire
• C. The leaves of the electroscope are negatively charged
• D. The knob of the electroscope is positively charged
• E. The electroscope has a net positive charge

Answer 1

Answer: (A)

The electroscope can be charged negatively without the positively charged rod touching the knob and using only a grounding wire

The negative charges from the leaves would be attracted to the rod and thus would accumulate at the knob side of the electroscope. Thus the leaves would be positively charged and the knob would be negatively charged.

If the electroscope is grounded, when the positively charged rod is brought near, the negative charges would collect at the knob, and the positive charges would flow out into the earth. Hence the electroscope could be charged negatively.