experiment of the refractive index

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Light Refraction Experiment

March 30, 2020 By Emma Vanstone Leave a Comment

This light refraction experiment might be one of the most simple to set up science experiments we’ve ever tried. It is a bit tricky to explain, but impressive even if you can’t quite get your head around it!

If you like this activity don’t forget to check out out our other easy science experiments for kids .

Materials for Light Refraction Experiment

Paper or card

Instructions

Fill the glass almost to the top.

Draw arrows on one piece of of card or paper. Place the paper behind the glass and watch as the arrow points the other way.

Now try to think of a word that still makes sense if you put it behind the glass.

We tried bud , the green ( badly drawn ) plant is on the opposite side when the paper is not behind the glass.

NOW works well too 🙂

How does this work?

Refraction ( bending of light ) happens when light travels between two mediums. In the refraction experiment above light travels from the arrow through the air, through the glass, the water, the glass again and air again before reaching your eyes.

The light reaching your eye (or in this case our camera) coming from the arrow is refracted through the glass of water. In fact the glass of water acts like a convex lens (like you might have in a magnifying glass). Convex lenses bend light to a focal point . This is the point at which the light from an object crosses.

The light that was at the tip of the arrow is now on the right side and the light on the right side is now on the left as far as your eye is concerned (assuming you are further away from the glass than the focal point.

If you move the arrow image closer to the glass than the focal point it will be the way around you expect it to be!

More Refraction experiments

Create an Alice in Wonderland themed version of this too!

Find out how to make your own magnifying glass .

We’ve also got a fun disappearing coin trick .

Or try our light maze to learn about reflection .

Last Updated on February 22, 2021 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

NOTIFICATIONS

Refraction of light.

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Refraction is the bending of light (it also happens with sound, water and other waves) as it passes from one transparent substance into another.

This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light. Without refraction, we wouldn’t be able to focus light onto our retina.

Change of speed causes change of direction

Light refracts whenever it travels at an angle into a substance with a different refractive index (optical density).

This change of direction is caused by a change in speed. For example, when light travels from air into water, it slows down, causing it to continue to travel at a different angle or direction.

How much does light bend?

The amount of bending depends on two things:

• Change in speed – if a substance causes the light to speed up or slow down more, it will refract (bend) more.
• Angle of the incident ray – if the light is entering the substance at a greater angle, the amount of refraction will also be more noticeable. On the other hand, if the light is entering the new substance from straight on (at 90° to the surface), the light will still slow down, but it won’t change direction at all.

Refractive index of some transparent substances

All angles are measured from an imaginary line drawn at 90° to the surface of the two substances This line is drawn as a dotted line and is called the normal.

If light enters any substance with a higher refractive index (such as from air into glass) it slows down. The light bends towards the normal line.

If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. The light bends away from the normal line.

A higher refractive index shows that light will slow down and change direction more as it enters the substance.

A lens is simply a curved block of glass or plastic. There are two kinds of lens.

A biconvex lens is thicker at the middle than it is at the edges. This is the kind of lens used for a magnifying glass. Parallel rays of light can be focused in to a focal point. A biconvex lens is called a converging lens.

A biconcave lens curves is thinner at the middle than it is at the edges. Light rays refract outwards (spread apart) as they enter the lens and again as they leave.

Refraction can create a spectrum

Isaac Newton performed a famous experiment using a triangular block of glass called a prism. He used sunlight shining in through his window to create a spectrum of colours on the opposite side of his room.

This experiment showed that white light is actually made of all the colours of the rainbow. These seven colours are remembered by the acronym ROY G BIV – red, orange, yellow, green, blue, indigo and violet.

Newton showed that each of these colours cannot be turned into other colours. He also showed that they can be recombined to make white light again.

The explanation for the colours separating out is that the light is made of waves. Red light has a longer wavelength than violet light. The refractive index for red light in glass is slightly different than for violet light. Violet light slows down even more than red light, so it is refracted at a slightly greater angle.

The refractive index of red light in glass is 1.513. The refractive index of violet light is 1.532. This slight difference is enough for the shorter wavelengths of light to be refracted more.

A rainbow is caused because each colour refracts at slightly different angles as it enters, reflects off the inside and then leaves each tiny drop of rain.

A rainbow is easy to create using a spray bottle and the sunshine. The centre of the circle of the rainbow will always be the shadow of your head on the ground.

The secondary rainbow that can sometimes be seen is caused by each ray of light reflecting twice on the inside of each droplet before it leaves. This second reflection causes the colours on the secondary rainbow to be reversed. Red is at the top for the primary rainbow, but in the secondary rainbow, red is at the bottom.

Activity ideas

Use these activities with your students to explore refration further:

• Investigating refraction and spearfishing – students aim spears at a model of a fish in a container of water. When they move their spears towards the fish, they miss!
• Angle of refraction calculator challenge – students choose two types of transparent substance. They then enter the angle of the incident ray in the spreadsheet calculator, and the angle of the refracted ray is calculated for them.
• Light and sight: true or false? – students participate in an interactive ‘true or false’ activity that highlights common alternative conceptions about light and sight. This activity can be done individually, in pairs or as a whole class .

Useful links

Learn more about different types of rainbows, how they are made and other atmospheric optical phenomena with this MetService blog and Science Kids post .

Learn more about human lenses, optics, photoreceptors and neural pathways that enable vision through this tutorial from Biology Online .

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Science Experiments

Cool Light Refraction Science Experiment – Arrow Changes Direction!

Magic trick? No, but the results of this experiment are pretty surprising. Kids (and adults) will stare in amazement and scratch their heads wondering what causes the arrow in this experiment to change direction right before their eyes! The secret is light refraction.

Exploring light refraction couldn’t be easier or more fun, simply preview the experiment with our demonstration video below and find an easy to understand explanation of how it works below.

JUMP TO SECTION:   Instructions  |  Video Tutorial  |  How it Works

Supplies Needed

• Piece of Paper

Light Refraction Science Lab Kit – Only $5

Use our easy Light Refraction Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Light Refraction Science Experiment Instructions

Step 1 – Get a sheet of paper and draw two arrows on it. One arrow near the top and one arrow near the bottom. Make the arrows point in the same direction.

Step 2 – Fill a glass with water.

Step 3 – Slowly lower the piece of paper behind the glass of water.

Step 4 –  Look through the glass of water and watch what happens. Do you know why the arrow appears to change directions? Find out the answer in the how does this experiment work section below.

Video Tutorial

How Does the Science Experiment Work

The scientific concept that is at work in this experiment is called refraction. Refraction is the bending of light. Refraction occurs when light travels from one medium to another (ie. air to water, water to air).

During the experiment, the light traveled from the image through the air, then through the glass cup into the water, and finally out of the glass cup and into the air once more before it reached our eyes. Light refracts as it passes from one medium to the next because it travels at different speeds through those mediums. Light travels fastest through air, a little slower through water, and even slower through glass.

This means that the light bends once when it travels through the glass cup into the water, and then it bends again when it travels out of the glass cup and into the air. As a result, the light paths cross and the image appears to be flipped horizontally (left/right).

Light Refraction Examples

The following are examples of refraction that occur all around us.

• Glasses or Contacts – The lenses of glasses and contacts are designed to bend light in ways that help a persons improve vision.
• Rainbow – Rainbows are formed when the rays of sunlight bend (refract) when they travel through rain drops.
• Cameras – A camera works because the lens causes the light rays to refract. 

More Experiments that Show Light Refraction

Refraction of Light Science Experiment – Watch as the straw appears to bend in this experiment that shows refraction in action.

Ruler Changes Size Science Experiment  – Observe how the size of an object changed when viewed through different liquids. 

I hope you enjoyed the experiment. Here are some printable instructions:

Light Refraction Science Experiment

Instructions.

• Get a sheet of paper, and draw two arrows on it. One arrow near the top and one arrow near the bottom. Make the arrows point in the same direction.
• Fill a glass with water.
• Slowly lower the piece of paper behind the glass of water.
• Look through the glass of water and watch what happens.

Reader Interactions

February 5, 2017 at 9:25 am

THIS IS COOL. MY DAUGHTER WON THE SCHOOL WIDE SCIENCE PROJECT. THANK YOU SO MUCH FOR DOING THIS EXPERIMENT!

April 20, 2018 at 3:07 pm

Cause of the reflection of the water.

September 10, 2019 at 11:45 am

*refraction

January 7, 2021 at 3:53 pm

I can’t get this to work. I have used a round glass and a square plastic container. I’ve moved the piece of paper close to the container of water and father back. I have lowered the paper quickly and very slowly. Clearly it works, so what am I missing? The size of the arrows? The size of the paper?

Help! I teach a science class to elementary school children and would love to do this. Please answer [email protected]

May 23, 2018 at 7:33 am

This is because of refraction

January 22, 2019 at 3:42 am

Wonderful. Thanks for sharing

May 29, 2019 at 8:03 am

It was very useful and unique. It impressed my teacher a lot.

January 7, 2021 at 4:11 pm

I was finally able to get the arrow to change direction, but it appears that the mechanism is not the water, but the shape of the glass. It did not work with a square or wide straight sided glass. It did work in a straight sided narrow glass, but the arrow was distorted and could be manipulated back and forth by moving the paper.

March 2, 2022 at 2:52 am

Wow, this helped me for my school project i won second place thank you so much

August 4, 2022 at 7:27 pm

I tried this in a square glass container and the arrow does not change direction.

Does the concave/convex shape of the glass have something to do with the result?

May 22, 2023 at 10:07 am

That’s a great question. Do you have multiple glass containers to try the experiment with? That way you can test to see if the shape of the contain changes the results of the experiment. If you try it, come back to let us know what you find.

July 31, 2023 at 6:30 pm

It was refraction that caused the change of direction

It is caused by the refraction or the shape of the glass.

September 28, 2023 at 6:22 am

Thnx, I got 3rd position in my competition! 🤤

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Disappearing Glass Rods

Glass objects are visible because they reflect some of the light that shines on them and bend or refract the light that shines through them. If you eliminate reflection from and refraction by a glass object, you can make that object disappear.

• Vegetable oil (we've found that Wesson brand works best; don't use "lite" oil)
• One or more Pyrex stirring rods or other small, clear glass objects, such as marbles, lenses, or test tubes
• Optional: Glass eye­dropper, glass magnifying lens

Pour some vegetable oil into the beaker.

Immerse a glass object in the oil. Notice that the object becomes more difficult to see. Only a ghostly image of the object remains. (Note: If you do this as a demonstration, keep your audience at a distance to make it harder for them to see the ghost object.)

Experiment with a variety of glass objects, such as clear marbles, lenses, and odd glassware. Some will disappear in the oil more completely than others.

You can make an eyedropper vanish before your eyes by immersing it and then sucking oil up into the dropper.

If you have a magnifying glass, immerse it in the oil. Notice that it does not magnify images when it is submerged.

You see a glass object because it both reflects and refracts light. When light traveling through air encounters a glass surface at an angle, some of the light reflects. The rest of the light keeps going, but it bends or refracts as it moves from the air to the glass.

When light passes from air into glass, it slows down. It’s this change in speed that causes the light to reflect and refract as it moves from one clear material (air) to another (glass). Every material has an index of refraction that is linked to the speed of light in the material. The higher a material’s index of refraction, the slower light travels in that material.

The smaller the difference in speed between two clear materials, the less reflection will occur at the boundary and the less refraction will occur for the transmitted light. If a transparent object is surrounded by another material that has the same index of refraction, then the speed of light will not change as it enters the object. No reflection and no refraction will take place, and the object will be invisible.

Wesson vegetable oil has nearly the same index of refraction (n) as Pyrex glass (n = 1.474). Different types of glass have different indices of refraction. In Wesson oil, Pyrex disappears, but other types of glass, such as crown glass or flint glass, remain visible. Fortunately for us, a great deal of laboratory glassware and home kitchen glassware is made from Pyrex glass.

For most Pyrex glass, the index-matching with Wesson oil is not perfect. That’s because Pyrex glass has internal strains that make its index of refraction vary at different places in the object. Even if you can match the index of refraction for one part of a Pyrex stirring rod, for example, the match will not be perfect for other parts of the rod. That’s why a ghostly image of the rod remains even with the best index matching.

The index of refraction of the oil (and of the glass, too) is a function of temperature. This demonstration will work better on some days than others.

Index of refraction is sometimes called optical density, but optical density is not the same as mass density. Two materials can have different mass densities even when they have the same index of refraction. Although Pyrex glass and Wesson oil have similar indices of refraction, Pyrex sinks in Wesson oil because it has a higher mass density than the oil. Wesson oil has a higher index of refraction than water (n = 1.33), but a lower mass density, so it floats on water. The index of refraction depends not only on density but also on the chemical composition of a material.

You can make Pyrex glass disappear by immersing it in glycerin or mineral oil. However, mineral oil comes in different weights, and each variety has a different index of refraction. To match the index of refraction of Pyrex glass, you’ll need a mixture of mineral oils of different weights. To create the proper mixture, place a Pyrex glass object into a large glass beaker and pour in enough heavy mineral oil to submerge it partially. Slowly add light mineral oil and stir. Watch the glass object as you pour. Most Pyrex glass will disappear when the mixture is two parts heavy mineral oil to one part light mineral oil. Notice the swirling refraction patterns as you mix the oils.

Karo syrup has an index of refraction close to that of glass. Karo can be diluted with water to match some types of glass. Other light-colored corn syrups may also work—you may want to experiment and find out.

Related Snacks

FREE K-12 standards-aligned STEM

curriculum for educators everywhere!

Find more at TeachEngineering.org .

• TeachEngineering
• Make That Invisible! Refractive Index Matching

Hands-on Activity Make That Invisible! Refractive Index Matching

Grade Level: 11 (9-12)

(can be split into four 50-minute sessions)

This activity also requires some non-expendable lab supplies and equipment that are all reusable if properly stored after the activity; see the Materials List for details.

Group Size: 4

Activity Dependency: None

Subject Areas: Physics

NGSS Performance Expectations:

TE Newsletter

Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, pre-req knowledge, introduction/motivation, vocabulary/definitions, troubleshooting tips, activity extensions, additional multimedia support, user comments & tips.

Refractive index is a fundamental optical property of materials, and knowing the accurate value of a material's refractive index enables us to predict the angle that light is bent as it passes through the material, which is important in many real-world applications. Chemical, environmental and biomedical engineers take advantage of refractive index matching to minimize (if not remove) multiple scattering when capturing images to study the properties and behavior of micro- and nano-sized particles (such as bacterial and colloidal systems). Optical engineers use accurate measurements of refractive index to design optical instrument components such as lenses, microscopes, telescopes as well as other equipment that utilize the properties of light. Mechanical engineers must know the refractive index of fluids and other materials to build efficient and affordable machines. These examples illustrate the importance of knowing and understanding the concept of refractive index. Numerous methods and modern instruments are available to accurately measure the refractive index of various materials.

After this activity, students should be able to:

• Determine the relationship of the angle of incidence and the angle of refraction between two different media.
• Measure the refractive index of a given liquid using Snell's law.
• Determine the refractive index of an unknown material using percent light transmission.

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

Ngss: next generation science standards - science.

Common Core State Standards - Math

View aligned curriculum

Do you agree with this alignment? Thanks for your feedback!

International Technology and Engineering Educators Association - Technology

State standards, texas - science.

For the teacher-led class demonstration:

• Disappearing Glass Demo Instructions
• two 500-ml clear glass beakers
• glycerin (or vegetable oil, such as Wesson; glycerin is preferred; see note below)
• 2 Pyrex stirring rods, such as the 12-inch clear glass stir rod available for $1.75 each at The Science Company website at https://www.sciencecompany.com/Clear-Glass-Stir-Rod-12-inch-P17256.aspx

Each group needs:

• poster board and writing utensils (or a small white board and a dry erase marker)
• Refractive Index Lab Worksheet
• (optional, for activity extension assignment) Refractive Index Application Research Questions

For Part 1, each group needs:

• laser pointer
• print out of a polar graph; such as the example graphs found at the University of South Florida's Florida Center for Instructional Technology ClipArtETC website at http://etc.usf.edu/clipart/43000/43018/polar_24-4l_43018.htm
• (optional but recommended) plastic sheet protector to protect the paper polar graph from spills
• semicircular hollow acrylic block, 12 cm diameter x 2.5 cm high, available (part# RCSC01) at Nova-Tech International at http://www.novatech-usa.com/RCSC01
• ~50 ml water
• ~50 ml glycerin (or vegetable oil, such as Wesson), such as ACS grade, 4-liter bottle of glycerin (catalog # S25342D) from Fischer at https://www.fishersci.com/shop/products/glycerin-4l-acs-grade/s25342d ; glycerin is preferred because it is the same color as water so students will not realize at first that the two liquids are different, and it is soluble in water, making clean-up easier

For Part 2, each group needs:

• LED lights/semiconductors (matching the color of the laser used), such as the LED semiconductors from Sargent Welch for a pack of five at https://sargentwelch.com/store/product/8887114/led-semiconductors
• 4 containers (cuvettes are preferred, but small test tubes also work)
• ~6 ml water
• ~6 ml glycerin (or vegetable oil, such as Wesson)
• 2 Pyrex glass tubes (~6 cm in length each) that fit in the sample container, as shown in Figure 2; such as "Rod, glass, Pyrex, 3 mm OD (outer diameter)," catalog # 239430, page 193 in University of Houston's Research Stores 2013 Catalog, for ~$1 per piece (~1.5 meter) at http://researchstores.nsm.uh.edu/catalog , Pyrex brand is necessary to get the desired results
• sample container rack or holder to securely hold vials of four samples, such as the one shown in Figure 2 made with cardboard, clear tape and two packing foam pieces
• electronic breadboard and electrical wire (optional but recommended to ensure the stability of the detector), such as the five mini solderless prototype breadboards with 170 tiepoints available for $6.67 at http://www.ebay.com/itm/5x-Transparent-Mini-Solderless-Prototype-Breadboard-170-Tie-points-for-Arduino-/231242048856?pt=LH_DefaultDomain_0&hash=item35d719a558 or www.amazon.com.

To share with the entire class:

• (optional but recommended if available) lux meter, to verify the reliability of the results from the homemade LED-multimeter light intensity detector; such as Mastech's light meter LX1010B, 50,000 Lux Luxmeter with LCD display for $15 (MSRP $50) at https://www.amazon.com/Light-Meter-LX1010B-Luxmeter-display/dp/B000JWUT6O

Student are expected to know:

• The basic properties of light, such as reflection, refraction, absorption, transmission and scattering.
• How to plot data points and determine the slope from the graph.
• The basic trigonometry (that is, the use of sine) for the calculation of refractive index using Snell's law.

(In advance, prepare to conduct a class demonstration, using the Disappearing Glass Demo Instructions as a guide, so the setup looks like Figure 1, with a stirring rod submerged in a beaker of water [left] and a stirring rod submerged in glycerin [right]. Write the challenge question on the classroom board. Then start by asking students the pre-assessment discussion questions, as described in the Assessment section. Then divide the class into groups of four and give each group a poster paper or small white board to write down its answers.)

What is the difference between transparent and invisible materials? (Listen to student answers.) Transparent material permits light to pass through it so that objects behind can be directly seen but the material itself is still visible to the naked eye. On the other hand, invisible material allows light to pass through as well, but it is not visible to our eyes.

Today, this is our challenge question : How can you make half of this stirring rod invisible without breaking it?

(Let students brainstorm and write down their final answers. Have each group share its answer and explain why. Summarize the answers on the classroom board.)

Let me show you one way of making half of the stirring rod disappear. (Demonstrate how to make half of the stirring rod disappear using two beakers, one with water and one with liquid glycerin.) What do you observe? (Students see examples of transparent and invisible materials, noticing that part of the rod submerged in glycerin appears to be invisible!)

(Expect some students to be fascinated. Others may have seen the demo but do not know the science behind it. Others may not believe it and examine the demo more carefully. Let students think about it and explore it for a few minutes. Then explain it.) If two materials have exactly the same refractive index (n), you cannot see the difference between the materials. Water has an n =1.33 while glycerin has n =1.47. A Pyrex stirring rod has n =1.47.

Light is very important in our lives. It travels in waves and has several unique properties—reflection, refraction, absorption, transmission and scattering. Light is the reason that we can see everything around us. However, have you ever thought that the unique properties of light could enable us to make something disappear? Before we get into making something "invisible," it is important for us to refresh our memories on what we mean by the refraction of light.

(Either introduce or review the concept of refraction.) Refraction is the bending of light as it passes from one medium to another. This behavior occurs because light changes speed when it travels into a different medium. Since light is used in a lot of research in science and engineering, it is important know how much light is refracting (or how much it changes its speed) in a given medium. Refractive index is one of the light optical properties that can be used to study the bending of light.

where c is the speed of light in a vacuum (3.0 x 10 8 m/s) and v is the speed of light in a certain medium. In other words, n is simply a way to know the speed of light in a medium relative to its speed in a vacuum. Based on current knowledge, we know of nothing faster than the speed of light in a vacuum.

(Give students a chance to think about their answers and then share what they are thinking).

For Part 1 of today's activity, we are going to use Snell's law to determine the index of refraction of an unknown liquid. A semi-circular hollow block is the container of your unknown liquid and you are going to change the angle of incidence of the laser beam at 5 o increments. Our first medium is the liquid and the second medium is the air. We will measure and record the angle of refraction in air. Then we will use the following relationship to determine the refractive index of the liquid ( n 1 ).

Snell's law is:

n 1 sinθ 1 = n 2 sinθ 2

If the second medium is air, we can assume that n 2 = 1:

n 1 sinθ 1 = sinθ 2

x = sin θ 1

n 1 sinθ 1 = sinθ 2 becomes y=n 1 x

Once you plot your data and the slope is determined, you can predict the identity of your unknown sample by referring to a list of known refractive indices of materials (Table 1).

Part 2 of the activity involves the refractive index matching of a material (a Pyrex glass tube) with two different liquids (water and glycerin). Refractive index matching is used by science and engineering researchers, such as in the analysis of colloidal system using imaging. The study of colloidal particle behavior has been important in the development of efficient and eco-friendly solutions to many energy and environmental challenges such as enhanced oil recovery, flow assurance, water management, and clean and efficient engines. Observing these systems in a micro- or nano-scale dimension using microscopes is not easy since they usually scatter light in all direction because the particles are so close to each other. Too much scattering makes the microscopic images blurry and unclear. (One way to minimize this is to reduce the concentration of the particles in a medium. However, lowering the concentration can reduce the signal being detected to observe the particles.) If the particles and the solvent have the same refractive index, light scattering is not a problem. Thus, refractive index matching is a significant tool enabling researchers to better observe what happens in experiments.

Refractive index matching is tested by determining the percent light transmission. The refractive index of the glass tube is matched to the refractive index of two different liquids. Recall what you observed in the "disappearing glass" demo. The stirring rod submerged in glycerin appeared to be invisible! In theory, if two materials have exactly the same refractive index, the light passes through without any (or minimal) scattering or refraction. The light travels straight because it cannot detect any difference in the two materials, hence the speed of the travelling light does not change (bend). Related to this, the higher the percent transmission of light in the sample with a glass tube in a liquid, we can assume that the glass tube has the same or close n of that liquid. In this activity, we will use an inexpensive and easy-to-build homemade detector for measuring the light intensity (in milliwatts).

Before the Activity

• Set up activity stations around the room with prepared samples for each team. The sample setup is shown in Figure 2, and an example station is shown in Figure 8. At each station, you may want to do steps 1 and 2 of Part 1 in advance of students arriving to conduct the activity.
• To ensure accurate data collection for Part 1, use clear tape to secure the semi-circular hollow block on the center of the polar graph. This minimizes movement of the block. Refer to Figures 5 and 7.
• For Part 2, set up the LED-multimeter detector as shown in Figure 6.
• If a lux meter is available, refer to the Refractive Index Lab Worksheet (Part 2, Analysis question #2) for information about the setup. This optional setup replaces the LED-multimeter detector with the lux meter. The percent transmission may not be the same since you are detecting light intensity in different units, but the trend will be similar.

With the Students—Part 1: Refractive Index Using a Hollow Cell

• Assign each group an "unknown" liquid. (Since students do not know that only samples of water and glycerin are available, give half of the class water and the other half glycerin.)
• Place the hollow semi-circular acrylic block filled with the group's assigned liquid at the center of the polar graph, as shown in Figure 4. If the polar graph is not protected by a plastic sheet, be careful not to get the paper wet!
• Use clear tape to secure the block to the graph. (Steps 1 and 2 may have already been done by the teacher.)
• Make sure that the laser pointer is working and lay it on the table so that the laser beam passes across the polar graph paper lying on the tabletop.
• Starting with the 0 o angle of incidence from normal (the line that is perpendicular to the flat edge of the block), rotate the graph paper at 5 o increments until the refracted ray totally disappears. (Refer to the setup in Figures 5 and 7.)
• Continue to change the angle of incidence by rotating the graph paper with the block, making sure that the light is always passing through the center point of the polar graph.
• Each time, record the angle of incidence ( θ 1 ) and angle of refraction ( θ 2 ).
• Take note of the angle at which the refracted ray totally disappears. This is called the total internal reflection. Teacher note: The critical angle (start of the total internal reflection) of light passing through water and air is 48.8° and for glycerin is 42.9°.
• Plot your data in terms of sin θ 2 vs. sin θ 1 . Determine the slope, which is the average refractive index. (Note: Recall Snell's law; n air = 1.00).

With the Students—Part 2. Refractive Index Matching Using Percent Light Transmission Measurement

• Your goal is to approximate the index of refraction of the glass tube based on the percent light transmission using a LED light and multimeter as the detector .

• Turn on the laser and the multimeter. Make sure that the laser beam is passing through the LED light. The light from the laser is converted to an electric signal that is read by the multimeter. Adjust the laser position and light height until you can detect the maximum signal in volts (V). Light intensity is directly proportional to the voltage you are reading. The LED light has a maximum output of ~1.0 V. After this step, DO NOT MOVE the laser or the detector while gathering data. Misalignment may give different results.
• Put the W1 sample container in between the laser and detector. Make sure the light is passing through the center of the sample container and the LED light.
• Determine the light intensity (in volts) after the laser passes through the sample. Record your data.
• Repeat steps 3-5 for samples W2, G1 and G2, recording the data.
• Calculate the percent transmission of light using the equation provided in Figure 8.
• Determine the refractive index of the glass tube based from the known data. For teacher reference, two methods are described below.

Method 1: Refractive Index Matching: Based on the percent light intensity equation, I is the light intensity that the multimeter is reading with the liquid and glass tube, while I o is the reading with pure liquid. If the glass tube has the same refractive index as the liquid in which it is submerged, the light passes through it without any refraction or scattering; thus, its percent light intensity is almost 100%. This method is commonly called "refractive index matching" and is typically used in situations in which it is hard to measure the refractive index of a certain substance, such as colloidal and bacterial systems.

Method 2: Another way to determine the refractive index is by using two sample containers, each with a different liquid. Measure the light intensity after the light passes through the container with liquid only. Then, submerge the Pyrex glass tube, then measure the light intensity passing through the sample container (now with glass tube and liquid). Follow with the same equation.

• Conclude the activity by having students answer the three lab reflection questions. Then collect the completed lab worksheets. If time permits, have students research and present to the rest of the class examples of real-world applications of refractive index applications used in science and engineering, as described in the Activity Extensions section.

absorption: A process in which light (energy) is transferred to a medium in which it is passing through.

angle of incidence: The angle measured between the normal and the incident light.

angle of refraction: The angle measured between the normal and the refracted light.

colloidal system: A system in which fine particles are dispersed within a continuous medium. A colloidal system may be solid, liquid or gas.

detector: A device that recovers or measures information.

normal: An imaginary line perpendicular to a surface.

reflection: The bouncing of light when it strikes a boundary between different media through which it cannot pass.

refraction: The bending of light as it passes from one medium to another.

refractive index: A number (optical property) that describes how light propagates through a medium.

scattering: The dispersal of rays of light when the light reflects from an unsmooth surface.

transmission: When light passes through a material and is not absorbed by that material.

Pre-Activity Assessment

Discussion Questions: To help students recall the common behaviors of light, give student pairs some time to discuss answers to the following questions. After the allotted time, have groups share their answers with the rest of the class. Answers to the following example questions are provided in the Pre-Activity Discussion Questions Answer Key .

• What is light?
• Light has the following behaviors when it is interacting with a certain boundary: reflection, refraction, absorption, transmission and scattering. For each, draw an example and use arrows to show how the light behaves.
• What is the difference between transparent and invisible?

Activity Embedded Assessment

Worksheets: During the course of the activity, have students complete the Refractive Index Lab Worksheet to show their understanding of the material as well as participation.

Post-Activity Assessment

Reflection Questions: At activity end, have students answer the three lab reflection summary questions and then turn in their completed lab worksheets. Review their answers to assess what they learned in the activity.

Safety Issues

• To keep the laser pointer from being pointed at people's eyes, use masking tape to secure the laser pointer in the setups before the activity begins.
• To prevent breakage and spills, place the activity glasses and liquids in a secure rack or container, such as the one shown in Figure 2 made from cardboard, tape and foam.

For Part 1, make sure that 1) the laser beam passes through the polar graph so students can see the incident and refracted beam clearly, 2) the light passes through the center point of the graph, and 3) the block is at the center of the polar graph.

For Part 2, make sure the LED-multimeter detector is stable during data collection. Moving any part of the detector after step 2 of Part 2 may give erroneous results. The electronic breadboard is helpful to avoid moving any detector part during the activity.

Knowing the refractive index of a material enables us to predict the angle that light is bent as it passes through the material, which is important in many real-world applications, such as the imaging of nano-sized particles by minimizing the scattering due to refraction, as well as the design of optical instruments and equipment that use light. Assign student teams to research real-world applications of refractive index matching in science and engineering. Hand out the Refractive Index Application Research Questions as a guide for their research. Give each group five minutes to present what they have researched in class in the form of a PowerPoint and/or poster presentations. Note: With so many applications to research, guide student teams to focus on one application as their topic, so as to not be overwhelmed with too much information.

For more information about total internal reflection (TIR):

• Applications of total internal reflection http://regentsprep.org/Regents/physics/phys04/captotint/
• Fiber Optic Cables: How They Work (5:35 minute video) https://www.youtube.com/watch?v=0MwMkBET_5I

Students learn about the basic properties of light and how light interacts with objects. They are introduced to the additive and subtractive color systems, and the phenomena of refraction. Students further explore the differences between the additive and subtractive color systems via predictions, ob...

Students learn about the science and math that explain light behavior, which engineers have exploited to create sunglasses. They examine tinted and polarized lenses, learn about light polarization, transmission, reflection, intensity, attenuation, and how different mediums reduce the intensities of ...

Contributors

Supporting program, acknowledgements.

Developed by the University of Houston's College of Engineering under National Science Foundation RET grant number 1130006. However, these contents do not necessarily represent the policies of the NSF and you should not assume endorsement by the federal government.

Last modified: December 11, 2020

practical physics

Sunday 26 june 2016, experiment 12: refractive index.

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Refractive Indices of Water and Oil: Lab Explained

• Refractive Indices of Water and…

1. AIM/ PURPOSE:

The aim of this experiment is pretty simple. It is to measure the refractive index of the light while it moves from one medium to another. Depending on the refractive indexes of both mediums, the angle of refraction will be at a greater or lesser angle. The angles are measured from the normal line , which is the line perpendicular to the meeting of both mediums. How to find the refraction index? There is a formula: n=c/v (which is speed of light in vacuum/ speed of light in material ). In our example of water and air, the light would refract away from the normal line. This occurs because of water slowing down the light, and this would cause the light to be bended which is equal to refraction. This can be verified by the use of Snell’s law which states that incident ray, refracted ray and normal line are all lying on the same plane. Snell’s law has a formula: sin(i)/sin(r) . To test and prove our hypothesis/theory we will fill up the container halfway with water, use a laser as a source of light and measure the angles. After the formula is applied we will be left with pretty accurate results.

2. RESEARCH QUESTION:

How to find/measure the refractive index of the material (in this case water and oil)? How are angles i (incident) and r (refractive) related? How to apply Snell’s law?

3. INTRODUCTION:

A container/ tank in a circular shape with angles is filled up halfway with a material (water and oil).

4. HYPOTHESIS/ PREDICTIONS:

Water’s refractive index will be equal to 1.333. We will also make a graph and a table.

5. PROCEDURE (DESCRIPTION OF THE EXPERIMENT):

We started with choosing a suitable circular container with angles which is used for refraction and filling it up with water. For the other container, we did the exact same thing but with oil. We connected the laser so that it was pointing right in the center and from different angles. Our tutor also mentioned that pointing the laser from beneath the container would give the same results, so we decided to examine that too. We took notes of the results. We found sin(i) and sin(r) separately. Then we divided them and got n (the refraction index). I then made a graph knowing that the slope=rise/rum=sin(i)/sin(r)=n. Units are very important in physics, but at the moment, in this experiment, the refractive index does not have a unit.

6. DATA AND ANALYSIS:

• Tools used: laser, laser refraction tank(a container with angles), scientific/ graphic calculator.
• The picture of the experiment and the tools:
• Data organized in a table:

• The calculations: Find the refractive angles
• Find sin (i) with a calculator
• Find sin (r) with a calculator

Divide the results in sin(i) by sin(r) and get the refractive index

The y-axis of the graph is sin (i). The x-axis of the graph is sin (r). How did I create the graph? I inserted my results from the table and applied them in google sheets. There is a formula for the slope or gradient of the graph, which is rise/rum; knowing that sin(i)/sin(r) is equal to that, we can find and draw the graph using the results.

Absolute uncertainty:

Formula- 𝚫x= (xmax- xmin)/2

Formula- x av = add all numbers and divide them by the number of numbers

sin(i) av =(0.174+0.342+0.5+0.643+0.766+0.866+0.94+0.985)/8≈ 0.652

sin(r) av =(0.122+0.259+0.358+0.485+0.588+0.656+0.707+0.743)/8≈ 0.490

n av =(1.4+1.3+1.4+1.3+1.3+1.3+1.3+1.3)/8≈ 1.33

𝚫sin(i) → (0.985-0.174)/2= 0.4055          0.652 ± 0.406

𝚫sin(r) → (0.743-0.122)/2=0.3105           0.490 ± 0.311

𝚫n → (1.4-1.3)/2=0.05                              1.33 ± 0.05

Fractional uncertainty:

0.406/0.652≈0.623

0.311/0.490≈0.635

0.05/1.33≈0.0376

Percentages uncertainty:

0.623×100%= 62.3%

0.635×100%= 63.5%

0.0376×100%= 3.76%

7. CONCLUSION AND EVALUATION:

Our hypothesis was proven to be correct. To conclude, we used formulas: sin(i)/sin(r) and rise/rum. It was very informative and taught us a lot. This is one of the foundation topics in the world of physics. The experiment was successful. We calculated the absolute uncertainty as in the last experiment. We found the refractive index, which is approximately 1.3 on average. We also made a graph using the table with the results.

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