Disappearing Beaker
Grade 5
Marci Howdyshell
References:
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http://www.education.com/science-fair/article/disappearing-beaker/
Science, Harcourt School Publishers, Ohio Student Ed. Grade 5
Objective:
Students will learn about light and why we see things. They will understand the vocabulary terms
reflection and refraction. They will be introduced to the term index of refraction just to understand that
different materials have different indices of refraction.
Materials:
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Mirrors – 1 per group/table to talk about reflection
1 beaker filled halfway with water
1 pencil
Two beakers per group: a larger one and a smaller one that fits inside the larger one. The smaller
one MUST be pyrex.
Vegetable oil (each group needs enough to fill the larger beaker about 3/4 full) – please return the
oil to the bottle after the experiment so we can reuse it!
Target Concept:
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Every material has an index of refraction. Usually, different materials have different indices of
refraction. However, in some cases two materials have the same indices of refraction.
When light passes through a material, it either reflects, refracts, or both. We see an object
because light reflects off of it. We can see an example of refraction when we look at an object
such as a pencil immersed in a glass of water. It will look bent because the light is bending as it
travels from air to glass to water.
If two objects have the same index of refraction, the light will not bend when it passes the
interface.
Procedure:
Reflection
1. Reflection is the bouncing of light from a surface. Light must be reflected from the surface of an
object in order for us to see the object. Discuss with the students what reflection is and draw a
picture on the board to describe a light ray bouncing off of an object.
2. Have 1 student per group pick up the mirror and look at themselves in it. Have them explain what
is going on in terms of reflection and light. What other objects can they see themselves reflected
in? (A very SMOOTH surface reflects light as an image in the surface rather than scattering it in
every direction).
Refraction
1. Refraction is the bending of light when it moves from one material to another. Every material has
something called an index of refraction. (Note that this is not a vocabulary word they need to
know, but it is valuable in this experiment. They will probably be unfamiliar with the term.)
When light travels from something with one index of refraction to something with a
different index of refraction, it bends, or refracts.
2. Have one student place the pencil in the beaker with water in it in the middle of the table. Every
student in the group should observe with their eyes what they see.
3. Have the students raise their hands and hold a class discussion about what they see. Can draw on
the board to describe how the pencil looks broken even though it is not because light refracts
when it passes from the air to the water.
Disappearing Beaker Experiment
1. Set all other supplies aside. Each group should have a smaller (pyrex) beaker and a larger beaker,
as well as some vegetable oil. You could give each group a different type of oil to see whose oil
works best. Have them write the materials in their lab notebooks.
2. Tell the students to place their smaller beaker in the larger beaker, and have one student slowly
begin to pour oil into the smaller beaker until it (just the small beaker) is full. All other students in
the group should be observing while the oil is poured.
3. Once the small beaker is full, have them record their observations.
4. Now have another student pour in more oil in so that the oil overflows into the larger beaker. All
other students in the group should be observing while the oil is being poured. They can pour the
oil until it fully covers the smaller beaker and record their observations.
5. Now give the students a chart of indices of refraction. Have them determine the index of
refraction of the beaker (tell them it is made of pyrex) and of the vegetable oil. Have them record
those in their lab notebooks. Based on what they know about indices of refraction, have them try
to explain what they see.
6. After they have shared what they think is going on, explain that light bends when it goes from
one index of refraction to another. However, for that to occur it must go through two different
indices of refraction. IF the index of refraction of the beaker is the SAME as that of the oil, then
the light going through it does not bend. It does not reflect either! To us, we cannot see the
beaker. This is because light needs to be reflected back to our eyes for us to see something. To
see an interface between two media, they must have different indices of refraction so that the light
will both refract and reflect back to our eyes.
7. Do not throw out the oil! Please return it to the bottle.
Target Observations:
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Students should notice that we can see the pyrex beaker if the larger beaker is filled with water. If
BOTH beakers are filled with vegetable oil, you cannot see the inner beaker.