为什么指南针的指针总是指向南北方向？
Why does a compass needle always point north-south?
地球本身像一个巨大磁体，地磁场对磁针施加力矩，使其顺着磁感线方向偏转。磁针北极被吸引指向地磁南极附近，也就是地理北方，所以能辨向。
Earth behaves like a giant magnet, and its field exerts a torque on the needle, turning it along the field lines. The needle's north pole is drawn toward the magnetic south near geographic north, so it indicates direction.
难度 专业 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
梁灿彬 等,《电磁学》,高等教育出版社,2004
Liang Canbin et al., Electromagnetism, Higher Education Press, 2004
#地磁场 #磁 #电磁物理
为什么冬天干燥时，脱毛衣或摸门把手更容易触电起静电？
Why are static shocks from clothes or doorknobs more common in dry winter air?
干燥空气导电差，摩擦产生的电荷不易通过空气或皮肤泄放，容易在体表积累。湿度高时水膜帮助电荷流失，静电就不明显。
Dry air conducts poorly, so charges from friction cannot easily leak away through air or skin and build up on the body. In humid conditions a water film helps discharge them, making static less noticeable.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
梁灿彬 等,《电磁学》,高等教育出版社,2004
Liang Canbin et al., Electromagnetism, Higher Education Press, 2004
#静电 #湿度 #电磁物理
为什么用塑料尺在头发上擦几下，就能吸起碎纸片？
Why can a plastic ruler rubbed on hair pick up bits of paper?
摩擦使尺子带上静电荷，靠近轻小的纸片时使纸片表面感应出相反电荷。异种电荷相吸，且纸片很轻，于是被尺子吸起来。
Rubbing charges the ruler with static electricity, and near light paper it induces opposite charges on the paper's surface. Opposite charges attract, and since the bits are light, they are lifted by the ruler.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
梁灿彬 等,《电磁学》,高等教育出版社,2004
Liang Canbin et al., Electromagnetism, Higher Education Press, 2004
#静电 #感应 #电磁物理
为什么装上电池，手电筒的小灯泡就会亮起来？
Why does a flashlight bulb light up when you put in batteries?
电池内部化学反应把化学能变成电能，形成电压驱动电子流过灯丝。电流让灯丝发热到白炽状态而发光，这就是电能转化为光和热。
A battery's chemical reaction turns chemical energy into electrical energy, creating a voltage that drives electrons through the filament. The current heats the filament to incandescence, converting electricity into light and heat.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
梁灿彬 等,《电磁学》,高等教育出版社,2004
Liang Canbin et al., Electromagnetism, Higher Education Press, 2004
#电流 #能量转化 #电磁物理
为什么磁铁能牢牢吸住铁钉，却吸不住铜钥匙？
Why does a magnet strongly attract an iron nail but not a copper key?
铁、镍、钴等铁磁性物质内部有可整齐排列的磁畴，在外磁场下被磁化而相吸。铜没有这种铁磁性，只产生极弱的感应，所以基本不被吸引。
Ferromagnetic materials like iron have magnetic domains that align in an external field and become magnetized, attracting the magnet. Copper lacks ferromagnetism and shows only a very weak induced response, so it is essentially not attracted.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
梁灿彬 等,《电磁学》,高等教育出版社,2004
Liang Canbin et al., Electromagnetism, Higher Education Press, 2004
#磁性 #铁磁 #电磁物理