Examkrackers question

[AKPsiMD84]

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This is Based on Physics 7th edition.
Topic: Light and Optics

I dont understand how to solve questions 169 and 173. Please help!

 

[niranjan162]

post the questions, some people dont have the books but can still help

 

[AKPsiMD84]

It has a picture so I scanned it for you. Question 173 was cut off but it basically gives you two points and asks what you should do to the lens to assure that the light will strike point A.

 

[AKPsiMD84]

anyone have an idea how to get to the answer?

 

[niranjan162]

I thought of it in more of a conceptual way as I dont think theres any equations that you could really use.

So this is how I thought about it. If you move the glass up or down its not gonna change the angle its hitting the glass and thus wont change the angle of refraction. So you can rule those two out.

IF you wanna tell me what the other two choices are cuz I cant read them I will tell you what I thought about those

 

[AKPsiMD84]

Sure, the other choices were to make the lens thinner or thicker.

 

[ThePandaFactor]

making the lens thicker will probably work

 

[AKPsiMD84]

Yea, thats the answer, what I don't understand is why and how do you figure that out?

 

[niranjan162]

well lets assume you made the lens thinner alot thinner, it wouldnt refract a second time and thus it, change only the angle the only one time and probably still hit b. So rule that out and u get make it thicker.

Not the best way but thats how I thought about it.

 

[ThePandaFactor]

Because the light travels slower in the high index material, so if it is thicker the light beam will travel at the refracted angle for longer and thus allow it to reach back to the target point.