Một khung dây hình tròn diện tích 10cm vuông, gồm 20 vòng dây. Khung dây đặt trong từ trường đều, vecto cảm ứng từ vuông góc với mặt phẳng; B=0.03T b) Quay khung 180 độ chung quanh 1 trong các đường kính của khung. Tính độ biến thiên từ thông qua khung. giúp mình với mng ưi!!!

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