Tiān-chû-pho
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Tiān-chû-pho (electromagnetic radiation) sī ū tiān-tiûⁿ (electric field) ham chû-tiûⁿ (magnetic field) tī khong-kan thoân-pò ê 1 chióng pho. Tiān-chû-pho mā hō chò tiān-chû hok-siā; lán pêng-sò͘ kóng ê kng, khêng-si̍t tō sī tiān-chû-pho. Tiān-tiûⁿ ham chû-tiûⁿ chiâⁿ-chò 90° teh hàiⁿ-tāng (oscillate), kap thoân-pò ê hong-hiòng mā lóng sio khiā-ti̍t.
Tiān-chû-pho ū lêng-liōng ham ūn-tōng-liōng, ē-tàng thoân hō͘ tú--tio̍h ê bu̍t-chit.