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1.0 Light travels in straight lines and illuminance decreases with distance from its source

​​​​Science 8 Optics and Vision.docx


Science 8 Unit II Guided Notes .docx

Rubric Science Optics and Vision.docx

Page 1 notes.pdf   Page 2 notes.pdf   Page 3 notes.pdf



Luminous intensity 
Light waves can travel through a vacuum, like outer space, and do not require a medium​ (unlike sound waves which require a medium). In empty space, the wave does not dissipate (grow smaller) no matter how far it travels, because the wave is not interacting with anything else. This is why light from distant stars can travel through space for billions of light-years and still reach us on earth. However, light can also travel within some materials, like glass and water. In this case, some light isabsorbed and lost as heat, just like sound. So, underwater, or in our atmosphere, light will only travel some finite range (which is different depending on the properties of the material it travels through).

How far is a light year?
A light-year is the distance light travels in one year. How far is that? Multiply the number of seconds in one year by the number of miles or kilometers that light travels in one second, and there you have it: one light-year. It's about 5.88 trillion miles (9.5 trillion km).