(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

1. When light travels from a material to air, total reflection occurs beyond 54 degrees. Calculate the index of refraction.

2. A converging lens has a focal length of 20 cm. When an object is placed at a certain disctance from the lens, a virtual image is created. How far from the lens is the object placed if the height of the image is 4 times greater than the object?

2. Relevant equations

1. sinC= n2/n1

2. ?

3. The attempt at a solution

1. I can use the equation, but I don't know how to calculate(?) the critical angle. I don't think any calculating is neccesary. The critical angle should be 45 (I'm not totaly sure) degrees, and my question is why?

2. I know that you have to place the object within the focal point to get a virtual image using a converging lens. And that tells us that the answer should be -something. But I don't know how to solve the equation... anyone that can by detail show me how to solve it? Answer should be di = -60

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# Homework Help: Optics, fast help needed

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