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Across 4. a transparent glass or plastic object with flat, polished sides 8. the range of electromagnetic radiation (2 wds) 9. a representation of an object 13. this type of radiation is used to sterilize surgical equipment (2 wds) 14. theory that states that white light is composed of different colours (wavelengths) of light (3 wds) 15. colour - wavelength of 400 nm 16. these wavelengths can penetrate human tissue but not bone 19. electromagnetic radiation that the eye can detect 21. colour - wavelength of 700 nm 22. the longest wavelength and lowest frequency - used in communication (2 wds) 23. according to this theory, matter selectively absorbs different colours or wavelengths of light (3 wds)

Down 1. a disturbance that transfers energy from one point to another without transferring matter 2. the distance between wave crests 3. is a wave pattern made of electric and magnetic fields that can travel through empty space (2 wds) 5. these wavelengths are used to heat food 6. the lowest point on a wave 7. the highest point on a wave 10. the range of different colours of light (2 wds) 11. we feel these wavelengths as heat (2 wds) 12. over exposure to this type of radiation can burn the skin and cause skin cancer (2 wds) 17. wave height 18. the rate of repetition of a wave 20. an attribute common to all substances or objects of the same group