Một dây dẫn đặt trong không khí có dòng điện I= 12A chạy qua, được gấp thành hình vuông cạnh a= 10cm. Xác định vectơ cường độ từ trường tại tâm O của hình vuông

Place several e-field sensors at a few points on different equipotential lines, and look at the relationship between the electric field and the equipotential lines. which statement is true? 1-at any point, the electric field is perpendicular to the equipotential line at that point, and it is directed toward lines of higher voltages. 2-at any point, the electric field is perpendicular to the equipotential line at that point, and it is directed toward lines of lower voltages. 3-at any point, the electric field is parallel to the equipotential line at that point.