Question
A student investigates how a negatively charged ebonite rod influences an uncharged electroscope as shown in the diagram at right.
(a) Write a step-by-step procedure of how the negatively charged ebonite rod could produce a positive charge on the electroscope. Other materials can be used, but none can be charged, and none can alter the charge of the ebonite rod.
(b) Referring to each step your procedure in part (a), describe or illustrate the movement of any relevant charge in the ebonite rod, electroscope and/or other materials used.
(c) Assume the student charges the electroscope. Describe how the negatively charged ebonite rod could be used to test whether the electroscope is positively charged. Also explain what the student should expect to observeand why.
▶️Answer/Explanation
Ans:
(a) 1. Bring ebonite rod near, but do not touch, the knob of the electroscope.
2. While keeping rod near, ground the electroscope with a finger or grounding wire.
3. While keeping rod near, remove finger or grounding wire.
4. Remove ebonite rod.
(b) 1. No change in ebonite rod, electrons repelled to the leaves of the electroscope.
2. Electrons exit the electroscope into the ground/earth.
3. No charge movement in either device.
4. Positive and negative charges in electroscope redistribute such that the electroscope has a net positive charge.
(c) Bring the negatively charged rod near the electroscope and look for attraction between the leaves; the positively charged leaves are attracted to the opposite charge.