एक अनंत रूप से लंबा, पतला सीधा तार समान रेखीय आवेश घनत्व λ = 4π × 10-2 C/m वहन करता है। तार के अक्ष से 20 mm की दूरी पर स्थित एक बिंदु पर विद्युत विस्थापन वेक्टर (electric displacement vector) D का परिमाण क्या 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?