標題:

CE Phy EM wave

發問:

Which of the following statements about ultra-violet ray is incorrect? A. UV is emitted from glowing fluorescent material. B. UV can give us a suntan C. Suntan oil protects us from over exposure to UV. D. A good pair of sun glasses should block UV as well as visible light Why A is incorrect?

最佳解答:

The answer is B. A is incorrect. It is the fluorescent material absorbsUV, then it emits visible light so that we can see the material. If UV isemitted instead, then we cannot see the material since it is not visible light. B is correct, it is a fact. C is incorrect. Suntan oil cannot protect us from overexposure to UV, it can only protect us from the damage of UV to our bodies. Oneshould prevent exposure to sunlight if he wants to prevent over exposuring toUV. D is incorrect. A good pair of sun glasses should onlyblock UV, not visible light. It is blocks visible light, then you cannot seewith your glasses and hence it is not a good pair of sun glasses.

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