1.咩野先可以叫做radioactive substance?如果是可以放射radiation的...咁會放射infra-red radiation 都叫radioactive??
2.interference會影響wave的speed or frequency??
3.如果光由shallow water to deep water wavelength 有分別??
4.點樣可以用experiment搵出concave lens 的focal length, please with detail explanation.