# Find the refractive index of different objects using Snell’s law

• australianschoolkid
In summary, the conversation is about conducting an experiment to find the refractive index of different objects using Snell's law. The objects chosen were ice, glass, and perspex, and three trials were taken for each. The speaker believes that the gradient of a line of best fit on a graph of their results will give the refractive index. They also ask about the significance of the angles of light leaving the prism. The other person replies that the gradient of a graph of the sine of the angles in air against the sine of the angles in the prism will give the refractive index. They suggest relabeling the data and plotting a graph to find the refractive index. The speaker asks for further clarification.

#### australianschoolkid

Hi
I have just conducted the experimental stage of a practical 'to find the refractive index of different objects using Snell’s law' (which states sine i/sine r =N). The objects chosen were Ice, Glass, and Perspex. As 3 trials were taken for all 3 objects, if these points were graphed, and a line of best fit was applied, I believe the gradient of this line would be the refractive index? Is this correct? Also does the I and R angles of the light leaving the prism hold any significance?

attached are my results.

RESULTS / DATA:

Perspex
I1 R1 N1 I2 R2 N2
40 25 -5.63 25 38.5 -0.18
10 8.5 -0.68 8.5 11.5 -0.91
29 20.5 -0.67 20.5 30 -1.01

Glass
I1 R1 N1 I2 R2 N2
22.5 13.5 -0.61 12.5 22.5 0.14
30.5 30 0.80 20 32.5 1.03
20 14 0.92 14 25 -7.48

Ice
I1 R1 N1 I2 R2 N2
22 31 0.02 30 34 -1.87
23 19 -5.65 19 24 -0.17
2 1.5 0.91 1.5 2 1.10

Note - The 1 results were those angles entering the prism, while the 2 results were those angles of the light leaving the prism.

cheers
matt

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You can obtain the index of refraction of the material of the prisma from the gradient of a graph of your data.

To do this relabel your data: $$I_1,\ R_2\ =\ \theta _a$$ and $$R_1,\ I_2\ =\ \theta _p$$, where the a refers to angles measured in air and the p refers to angles measured inside of the prisma.

The gradient of a graph of the sine of the angles in air against the sine of the angles in the prisma will then give the refractive index of the material. This follows from Snell's law.

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Thanks

Thanks heaps for replying, when you tell me to relabel my data as $$I_1,\ R_2\ =\ \theta _a$$, what does the "," represent? is this some sort of function between the two?

Matt

no its just like that there is not funtction in that

so could you please explain what he's saying?

how I've been graphing so far

this is what I've done, is this correct? so if i take the gradient this shall be the refactive index?

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hi i was wondering if you could please help me with the graphing of snell's law, as I've been told you can graph somthing over somthing and the gradient of this line is the refactive index, are you able to assist as I am quite confused as the current results i am getting are quite wrong!

cheers matt

Sorry my explanations are clear only to me. Let's try again.

Instead of labelling your data values as $$I_1\ and\ R_2$$ label them as $$\theta _a$$, that is these angles are the angles measured in air.

Change your labelling for the $$R_1\ and\ I_2$$ angles to $$\theta _p$$, that is these are the angles measured inside the material of the prisma.

Then plot a graph of $$\sin(\theta _a)$$ as a function of $$\sin(\theta _p)$$.

The gradient of such graph will be the index of refraction of the prisma material. Hope this makes it clearer.

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## 1. What is Snell's law?

Snell's law is a formula that describes the relationship between the angle of incidence and the angle of refraction for a light ray passing through a boundary between two different mediums.

## 2. How is Snell's law used to find the refractive index of an object?

Snell's law can be rearranged to solve for the refractive index of a material by dividing the sine of the angle of incidence by the sine of the angle of refraction. The result will be the refractive index of the material.

## 3. What are the materials needed to conduct an experiment to find the refractive index of an object?

You will need a light source, a protractor, a ruler, a transparent object (such as a glass block or plastic prism), and a medium to place the object in (such as air or water).

## 4. How do you measure the angle of incidence and angle of refraction?

Using the protractor, measure the angle of incidence as the angle between the incoming light ray and the normal line (perpendicular line) to the surface of the object. Then, measure the angle of refraction as the angle between the refracted light ray and the normal line.

## 5. Why is it important to find the refractive index of different objects?

The refractive index of a material determines how light will behave when passing through it, such as how much the light will bend or change direction. This is important in many scientific and technological applications, such as designing lenses for cameras and glasses, understanding the behavior of light in different environments, and studying the properties of different materials.