https://blog.gongquiz.com/2022/08/15/%ec%9e%90%ec%86%8d%eb%b0%80%eb%8f%84magnetic-flux-density%ec%97%90-%eb%8c%80%ed%95%9c-%ec%84%a4%eb%aa%85%ec%9c%bc%eb%a1%9c-%eb%a7%9e%eb%8a%94-%ea%b2%83%ec%9d%80-%ec%9e%90%ea%b8%b0%eb%b9%84/