# Critical angle

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I had done:

1.96/2.03 = 0.97 = refractive index

since 1/sinC = refractive index, I tried to find the critical angle but the maximum value of sin is 1 so it didn't work!

How should I go about this question?? Can someone please explain it to me in simple terms. Furthermore, why is 1/sinC = refractive index??

The equatioin is refractive index = sin i/sin r

Since at the critical angle, sin r is 90, shouldn't it be sin i = refractive index?

1.96/2.03 = 0.97 = refractive index

since 1/sinC = refractive index, I tried to find the critical angle but the maximum value of sin is 1 so it didn't work!

How should I go about this question?? Can someone please explain it to me in simple terms. Furthermore, why is 1/sinC = refractive index??

The equatioin is refractive index = sin i/sin r

Since at the critical angle, sin r is 90, shouldn't it be sin i = refractive index?

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#2

To find the critical angle of a material, you have to go from the denser medium, so i is actually r and r is actually i. So you can either swap them around or do sin(r)/sin(i) = sin(c)

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(Original post by

To find the critical angle of a material, you have to go from the denser medium, so i is actually r and r is actually i. So you can either swap them around or do sin(r)/sin(i) = sin(c)

**mclean_tom_**)To find the critical angle of a material, you have to go from the denser medium, so i is actually r and r is actually i. So you can either swap them around or do sin(r)/sin(i) = sin(c)

And when it says "refractive index of glass", which one out of the incident angle and refractive angle is the angle fir glass? This always confuses me

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#4

If you are doing the critical angle, you have to go from the denser medium. So in this one, you have to do

Refractive index = 2.03/1.96 = 1.036

If you think about it, the refractive index has to be bigger than 1 because the light is slowing down.

Then, you can use sin(i) = 1 / 1.03

i = sin-1(1/1.03) = 75º

Remember, in critical angles you have to go from the denser medium and that sin(r) = 1 because r = 90.

Refractive index = 2.03/1.96 = 1.036

If you think about it, the refractive index has to be bigger than 1 because the light is slowing down.

Then, you can use sin(i) = 1 / 1.03

i = sin-1(1/1.03) = 75º

Remember, in critical angles you have to go from the denser medium and that sin(r) = 1 because r = 90.

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(Original post by

If you are doing the critical angle, you have to go from the denser medium. So in this one, you have to do

Refractive index = 2.03/1.96 = 1.036

If you think about it, the refractive index has to be bigger than 1 because the light is slowing down.

Then, you can use sin(i) = 1 / 1.03

i = sin-1(1/1.03) = 75º

Remember, in critical angles you have to go from the denser medium and that sin(r) = 1 because r = 90.

**mclean_tom_**)If you are doing the critical angle, you have to go from the denser medium. So in this one, you have to do

Refractive index = 2.03/1.96 = 1.036

If you think about it, the refractive index has to be bigger than 1 because the light is slowing down.

Then, you can use sin(i) = 1 / 1.03

i = sin-1(1/1.03) = 75º

Remember, in critical angles you have to go from the denser medium and that sin(r) = 1 because r = 90.

But in other questions when it says "the refractive angle of glass", is glass the 2nd medium? Like, in the equation sin i/sin r, is r the angle to the normal for the glass?

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#6

(Original post by

Yes, i understood that, thanks.

But in other questions when it says "the refractive angle of glass", is glass the 2nd medium? Like, in the equation sin i/sin r, is r the angle to the normal for the glass?

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**jtbteddy**)Yes, i understood that, thanks.

But in other questions when it says "the refractive angle of glass", is glass the 2nd medium? Like, in the equation sin i/sin r, is r the angle to the normal for the glass?

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If you get a number bigger than 1 for refractive index, you are most likely correct

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#7

When you're just given the refractive index, it's the index from a vacuum into that material. Also the same as the speed of light in a vacuum divided by the speed of light in that material. Critical angle is the incident angle required to give a 90 degree refraction (and thus go along the normal)

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(Original post by

Yes

If you get a number bigger than 1 for refractive index, you are most likely correct

**mclean_tom_**)Yes

If you get a number bigger than 1 for refractive index, you are most likely correct

(Original post by

When you're just given the refractive index, it's the index from a vacuum into that material. Also the same as the speed of light in a vacuum divided by the speed of light in that material. Critical angle is the incident angle required to give a 90 degree refraction (and thus go along the normal)

**lerjj**)When you're just given the refractive index, it's the index from a vacuum into that material. Also the same as the speed of light in a vacuum divided by the speed of light in that material. Critical angle is the incident angle required to give a 90 degree refraction (and thus go along the normal)

So in this example, medium 1 is air, and medium 2 is the plastic layer and it's called "the refractive index of the plastic layer"?

My question is, when it says "the refractive index of x", x is always the 2nd medium right?

In this question, could you help me draw the line outside the prism? I know that for a denser solution, the line inside the prism will be closer to the normal, but how is it meant to be drawn out of the prism?

Thanks for your help

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#9

(Original post by

So in this example, medium 1 is air, and medium 2 is the plastic layer and it's called "the refractive index of the plastic layer"?

My question is, when it says "the refractive index of x", x is always the 2nd medium right?

In this question, could you help me draw the line outside the prism? I know that for a denser solution, the line inside the prism will be closer to the normal, but how is it meant to be drawn out of the prism?

Thanks for your help

**jtbteddy**)So in this example, medium 1 is air, and medium 2 is the plastic layer and it's called "the refractive index of the plastic layer"?

My question is, when it says "the refractive index of x", x is always the 2nd medium right?

In this question, could you help me draw the line outside the prism? I know that for a denser solution, the line inside the prism will be closer to the normal, but how is it meant to be drawn out of the prism?

Thanks for your help

If you're still stuck I'll help you later

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(Original post by

Do you know Snell's law? If you do you should be able to work this out by yourself. You can make up numbers for the refractive index and draw out the answers if you want as long as the denser medium (high sugar conc.) has a larger refractive index than the lower medium (low sugar conc.)

If you're still stuck I'll help you later

**lerjj**)Do you know Snell's law? If you do you should be able to work this out by yourself. You can make up numbers for the refractive index and draw out the answers if you want as long as the denser medium (high sugar conc.) has a larger refractive index than the lower medium (low sugar conc.)

If you're still stuck I'll help you later

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#11

The more concentrated solution has a higher refractive index lower speed of light.

Does that help? I can probably go through it for you, but it would be better if you went through it using Snell's law to see how that different angles change.

Does that help? I can probably go through it for you, but it would be better if you went through it using Snell's law to see how that different angles change.

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(Original post by

The more concentrated solution has a higher refractive index lower speed of light.

Does that help? I can probably go through it for you, but it would be better if you went through it using Snell's law to see how that different angles change.

**lerjj**)The more concentrated solution has a higher refractive index lower speed of light.

Does that help? I can probably go through it for you, but it would be better if you went through it using Snell's law to see how that different angles change.

Since refractive index = v1/v2, that explains why it has a lower speed?

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#13

**jtbteddy**)

Refractive index is a measure of how close the path is to the normal right? So the more concentrated solution will have a path closer to the normal?

Since refractive index = v1/v2, that explains why it has a lower speed?

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#15

(Original post by

Kkay, thanks. But is refractive index a measure of how close the path is to the normal?

**jtbteddy**)Kkay, thanks. But is refractive index a measure of how close the path is to the normal?

more dense to less dense--> away from normal.

So to answer the original question with the prism, the refraction will be greater both entering and exiting, which means that it will first move more towards and later more away from the normal. Does that make sense?

P.s. check that using snell's law because I haven't drawn out the diagram personally.

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(Original post by

No, not really, it's a measure of how much refraction takes place. Less dense to more dense--> towards the normal

more dense to less dense--> away from normal.

So to answer the original question with the prism, the refraction will be greater both entering and exiting, which means that it will first move more towards and later more away from the normal. Does that make sense?

P.s. check that using snell's law because I haven't drawn out the diagram personally.

**lerjj**)No, not really, it's a measure of how much refraction takes place. Less dense to more dense--> towards the normal

more dense to less dense--> away from normal.

So to answer the original question with the prism, the refraction will be greater both entering and exiting, which means that it will first move more towards and later more away from the normal. Does that make sense?

P.s. check that using snell's law because I haven't drawn out the diagram personally.

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**lerjj**)

No, not really, it's a measure of how much refraction takes place. Less dense to more dense--> towards the normal

more dense to less dense--> away from normal.

So to answer the original question with the prism, the refraction will be greater both entering and exiting, which means that it will first move more towards and later more away from the normal. Does that make sense?

P.s. check that using snell's law because I haven't drawn out the diagram personally.

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#18

(Original post by

Nvm. Got it. Thanks

**jtbteddy**)Nvm. Got it. Thanks

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(Original post by

Do you want help with that question as well? I think violet light refracts more strongly than red light.

**lerjj**)Do you want help with that question as well? I think violet light refracts more strongly than red light.

Violet refracts the most, i.e. Its angle of refraction is the smallest.

Got it thanks!

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#20

(Original post by

Yupp, youre right:

Violet refracts the most, i.e. Its angle of refraction is the smallest.

Got it thanks!

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**jtbteddy**)Yupp, youre right:

Violet refracts the most, i.e. Its angle of refraction is the smallest.

Got it thanks!

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But yeah, that diagram is perfect so just use that for all future queries re refraction.

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