Cho mạch điện có điện trở R =50 Ω , cho dòng điện có cường độ 1,8A qua điện trở . a) tính hđt của nguồn điện . b) thay R bằng R' khi đó cđdđ qua R' giảm ba lần tính R' . c) thay R băng R'' = 15 Ω khi đó cđdđ qua R'' là bao nhiêu?

Ametal ring 4.20 cm in diameter is placed between the north and south poles of large magnets with the plane of its area perpendicular to the magnetic field. these magnets produce an initial uniform field of 1.12 t between them but are gradually pulled apart, causing this field to remain uniform but decrease steadily at 0.240 t/s . (a) what is the magnitude of the electric field induced in the ring? (b) in which direction (clockwise or counterclockwise) does the current flow as viewed by someone on the south pole of the magnet?