Trong từ trường đều có cường độ H = 1000A/m, xét một diện tích phẳng S = 50cm2, sao cho các đường sức từ tạo với mặt phẳng của diện tích S một góc 300. Tính từ thông gởi qua diện tích đó

measure their densities same density, same sub

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me