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Light is incident upon a piece of Crown Glass at an angle of 50°, what is the angle of refraction when it passes to air?

I keep getting error when I type it on my calculator is this a trick question?

I keep getting error when I type it on my calculator is this a trick question?

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#2

(Original post by

Light is incident upon a piece of Crown Glass at an angle of 50°, what is the angle of refraction when it passes to air?

I keep getting error when I type it on my calculator is this a trick question?

**onionnn**)Light is incident upon a piece of Crown Glass at an angle of 50°, what is the angle of refraction when it passes to air?

I keep getting error when I type it on my calculator is this a trick question?

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#4

**onionnn**)

Light is incident upon a piece of Crown Glass at an angle of 50°, what is the angle of refraction when it passes to air?

I keep getting error when I type it on my calculator is this a trick question?

n1sinø1 = n2sinø2

Refractive index :

air -- n=1.0

crown glass -- n = 1.52

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the refractive index for crown glass I was given was 1.51

n1sinø1 = n2sinø2

1.51xsin(50)=1xsinø2

sin-1=1.51xsin(50)/1

error

n1sinø1 = n2sinø2

1.51xsin(50)=1xsinø2

sin-1=1.51xsin(50)/1

error

Last edited by onionnn; 5 months ago

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#6

(Original post by

the refractive index for crown glass I was given was 1.51

n1sinø1 = n2sinø2

1.51xsin(50)=1xsinø2

sin-1=1.51xsin(50)

error

**onionnn**)the refractive index for crown glass I was given was 1.51

n1sinø1 = n2sinø2

1.51xsin(50)=1xsinø2

sin-1=1.51xsin(50)

error

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yes that is what the question is asking the light is passing from crown glass to air

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#8

(Original post by

yes that is what the question is asking the light is passing from crown glass to air

**onionnn**)yes that is what the question is asking the light is passing from crown glass to air

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(Original post by

So what is total internal reflection and when does it happen ?

**Mr Wednesday**)So what is total internal reflection and when does it happen ?

does that make the angle of refraction 90? I'm not sure

anyhow I've already tried to type that answer into the answer box but its still saying incorrect

Last edited by onionnn; 5 months ago

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#10

(Original post by

TIR happens when n1>n2 and i>c

does that make the angle of refraction 90? I'm not sure

anyhow I've already tried to type that answer into the answer box but its still saying incorrect

**onionnn**)TIR happens when n1>n2 and i>c

does that make the angle of refraction 90? I'm not sure

anyhow I've already tried to type that answer into the answer box but its still saying incorrect

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(Original post by

Ok, for your situation you clearly have n1 > n2. Next you need to calculate the critical angle and see if it is bigger or smaller than the incidence angle. BTW for problems like this its ALWAYS a good idea to show a diagram to make sure you defined the angles in the right way

**Mr Wednesday**)Ok, for your situation you clearly have n1 > n2. Next you need to calculate the critical angle and see if it is bigger or smaller than the incidence angle. BTW for problems like this its ALWAYS a good idea to show a diagram to make sure you defined the angles in the right way

relative to the normal.

I have tried to answer the question to two significant figures which gives 42 but its still saying incorrect

Last edited by onionnn; 5 months ago

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#12

(Original post by

sinøc=n2/n1 sin-1=1/1.51 =41.47

**onionnn**)sinøc=n2/n1 sin-1=1/1.51 =41.47

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(Original post by

Ok, two thing here, if you want to type a "power", best to use a ^ sign so its clear that sin^-1 is inverse sin, and not sin minus 1. If your input angle is > critical angle then what happens to the light ray, does it refract ?

**Mr Wednesday**)Ok, two thing here, if you want to type a "power", best to use a ^ sign so its clear that sin^-1 is inverse sin, and not sin minus 1. If your input angle is > critical angle then what happens to the light ray, does it refract ?

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#15

(Original post by

does that mean TIR occurs and doesn't refract?

**onionnn**)does that mean TIR occurs and doesn't refract?

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(Original post by

Yup, it cannot refract so has to reflect instead to obey energy and momentum conservation - we just invented the optical fibre - YAY !

**Mr Wednesday**)Yup, it cannot refract so has to reflect instead to obey energy and momentum conservation - we just invented the optical fibre - YAY !

i have also posted a picture of the question above for you to check if I misunderstood the question and worded it wrong

Last edited by onionnn; 5 months ago

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#17

(Original post by

does that mean TIR occurs and doesn't refract?

**onionnn**)does that mean TIR occurs and doesn't refract?

(Original post by

unfortunately, I have to type in an answer and I've tried 0.00 degrees since it requires a two significant figures answers and it asks me to try again, and this came up: An angle of 0∘ means that the light would be travelling perpendicularly away from the interface. Is that what you meant? If it is, then take another look at your equation, you may have got some values wrong.

**onionnn**)unfortunately, I have to type in an answer and I've tried 0.00 degrees since it requires a two significant figures answers and it asks me to try again, and this came up: An angle of 0∘ means that the light would be travelling perpendicularly away from the interface. Is that what you meant? If it is, then take another look at your equation, you may have got some values wrong.

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(Original post by

Yup, it cannot refract so has to reflect instead to obey energy and momentum conservation - we just invented the optical fibre - YAY !

Ok, try an angle relative to the surface normal that represents the ray reflecting back into the glass in that case. You might end up with a negative angle if so, thats fine physically.

**Mr Wednesday**)Yup, it cannot refract so has to reflect instead to obey energy and momentum conservation - we just invented the optical fibre - YAY !

Ok, try an angle relative to the surface normal that represents the ray reflecting back into the glass in that case. You might end up with a negative angle if so, thats fine physically.

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#19

(Original post by

and what might that be? could you give me an example?

**onionnn**)and what might that be? could you give me an example?

https://www.youtube.com/watch?v=0MwMkBET_5I

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(Original post by

Optical fibre uses TIR to guide light over long distances - pretty much the entire internet is carried that way.

https://www.youtube.com/watch?v=0MwMkBET_5I

**Mr Wednesday**)Optical fibre uses TIR to guide light over long distances - pretty much the entire internet is carried that way.

https://www.youtube.com/watch?v=0MwMkBET_5I

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