: Các dòng điện I1 = 4 A, I2 = 6 A chạy cùng chiều trong hai dây dẫn thẳng, rất dài, song song và cách nhau 10 cm. Vectơ từ trường do hai dòng điện
này gây ra tại một điểm nằm trên mặt phẳng chứa các dòng điện và cách đều
chúng sẽ:
A. hướng thẳng đứng lên trên và có độ lớn 8.10-6 T
B. hướng thẳng đứng xuống dưới và có độ lớn 9.10-6 T.
C. bằng 0.
D. hướng thẳng đứng lên trên và có độ lớn 10.10-6 T

Abug is 12 cm from the center of a turntable that is rotating with a frequency of 45 rev/min . what minimum coefficient friction is required so that the bug stays on the turntable?

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?

What is a possible result of higher air temperature caused by global warming