समान आवेश वाली दो पिथ गेंदे (pith balls) समान लंबाई की डोरियों द्वारा एक उभयनिष्ठ बिंदु से लटकाई गई हैं, और उनके बीच साम्यावस्था दूरी r है। अब, यदि डोरियों को मूल ऊंचाई की आधी ऊंचाई पर दृढ़ता से क्लैंप कर दिया जाता है, तो गेंदों के बीच नई साम्यावस्था दूरी हो जाती है:

Which of the following statements are correct regarding electrostatic properties of conductors? A. Inside a conductor, the electrostatic field is zero. B. Electric field at the surface of a charged conductor does not depend on its surface charge density. C. The interior of a charged conductor can have no excess charge in static conditions. D. At the surface of a charged conductor, the electrostatic field must be normal to the surface at every point. E. The electrostatic potential is zero everywhere inside a charged conductor. Choose the correct answer:

What type of electric charge is acquired by a glass rod when it is rubbed with a silk cloth?