Xác định điện trở nối đất của hệ thống nối đất gồm 4 cọc thép bọc đồng có đường kính mỗi cọc 16mm, mỗi cọc dài 2m, cọc bố trí thành dãy, chôn sâu 0.8m so với mặt đất, khoảng cách giữa hai cọc là 6m. Cáp liên kết giữa các cọc là cáp đồng trần tiết diện 50mm2. Điện trở suất của đất đo vào mùa khô

To create electromagnetic induction, which of the following has to move? a. a wire b. a magnet c. a transformer d. either a or b

Search coils and credit cards. one practical way to measure magnetic field strength uses a small, closely wound coil called a search coil. the coil is initially held with its plane perpendicular to a magnetic field. the coil is then either quickly rotated a quarter-turn about a diameter or quickly pulled out of the field. (a) derive the equation relating the total charge q that flows through a search coil to the magnetic-field magnitude b. the search coil has n turns, each with area a, and the flux through the coil is decreased from its initial maximum value to zero in a time ∆t. the resistance of the coil is r, and the total charge is q = i∆t, where i is the average current induced by the change in flux. (b) in a credit card reader, the magnetic strip on the back of a credit card is rapidly “swiped” past a coil within the reader. explain, using the same ideas that underlie the operation of a search coil, how the reader can decode the information stored in the pattern of magnetization on the strip. (c) is it necessary that the credit card be “swiped” through the reader at exactly the right speed? why or why not?

True or false graphs must include scales that increase by the same amount