# Engineering Library Scopes

In this unit, students focus on light energy, investigating the science phenomena of how light moves when it interacts with different kinds of matter. Students use scientific knowledge about light to engineer a device that uses mirrors to redirect light. This page is a high-level extract of this lesson.

## Science Background for Teachers:

The science background section gives teachers more in-depth information about the phenomena students explore in this unit on light energy and matter. Here is an excerpt from the science background information on engineering library scopes.

Almost all objects reflect some light. This is how we see. Sight is a sense that uses the eyes to take in light information about an object’s position, shape, and color. Light rays reflect off of the object in all directions and into our eyes.

The incoming ray of light is called an incident ray. The outgoing ray is called a reflected ray, and the direction that it travels follows a predictable pattern. It always reflects off of the surface at an identical angle as the incident ray but on the opposite side of an imaginary line at a right angle to the mirror, located at the point where the rays meet. This is called the law of reflection.

Light is always reflected in this way. However, the properties of the material light reflect off of affect how we see the object. Think of a mirror. The surface of the mirror is so smooth and reflective that you can see your image in it. This happens because the incident rays of light are reflected off of the smooth surface in the same pattern in which they arrived.

With a rougher surface, the light rays are reflected in many directions. This is because the roughness of the surface means that each ray of light hits the surface at a different orientation. Each ray still follows the law of reflection, but the roughness of the surface causes the reflected rays to scatter in different directions.

How light behaves depends on the medium with which it is interacting. Some materials are more reflective or absorbent than others. For example, dark-colored surfaces absorb more light and reflect less light than light-colored surfaces. This is why dark-colored objects warm up more than light-colored objects.

An object’s color also depends on how light is reflected and absorbed from a surface. This is because an object’s color is not within the object itself. Instead, the color of an object is determined by how that object interacts with light and then reflects or absorbs it.

When visible light hits an object, different frequencies are absorbed and reflected. For example, a strawberry is red because it absorbs all of the frequencies of visible light that shine on it except for the frequency associated with red. The frequency associated with red reflects off of the strawberry and into our eyes, which is why we see strawberries as red.

Black and white are not actually colors because they don’t have a specific wavelength. Black objects absorb all wavelengths of light and convert them into heat. In contrast, white objects reflect all wavelengths of light.

In addition to color, another property of matter is how much light passes through it. Some materials are transparent because they allow almost all light to pass through to the other side, which means almost no light reflects off them. Instead, it is slightly refracted. Some materials are translucent, which means some light passes through and some is blocked. This makes objects on the other side appear blurry. Most materials are opaque, which means they block all light from passing through, either reflecting or absorbing the light. When an object has a shadow, it is evidence that the object is opaque because it has blocked the light from passing through.

Once architects and engineers understand how light behaves with different kinds of materials, they can then select those materials that have the properties best suited for their desired function.

For example, the Bronx Library Center’s eastern wall is made up almost entirely of glass, which allows sunlight to stream through because glass is transparent, increasing the amount of natural light that reaches inside the library. The glass walls are also specially designed for their insulating properties so they help to keep the space from getting too hot or too cold.

Although the glass wall allows a lot of light to enter the library, this light is strongest right next to the window. The designers of the Bronx Library Center wanted to spread out the light so it illuminated a greater area. Their solution was special “light shelves” in front of part of the windows that reflect light off of them and up to the ceiling. The ceiling redirects the path of the sunlight by reflecting it deeper into the room.

Light shelves are just one technology that people have developed to redirect light. Periscopes are another example of this because they use two mirrors to bounce light from one place to another. A typical periscope has each mirror angled at 45 degrees to the direction you want to see. The light reflects off of one mirror to the other and then out to your eye. Periscopes are often used in submarines so the crew can see above the water without having to come to the surface.

## Science Lesson: Engineering Library Scopes

Students continue to figure out different phenomena related to forms of energy, focusing in this unit on light energy and how light interacts with different kinds of matter. In this lesson, students apply their knowledge of light energy and matter to figure out how to engineer a hand-held device that uses mirrors to redirect light so a viewer can see in front of and above their heads.

## Science Big Ideas

• Light is a form of kinetic energy and the Sun is the largest source of light on Earth.
• The ray model describes how light moves in straight-line paths called light rays. Whenever you see a narrow beam of light, it is actually a bundle of many parallel light rays.
• Whenever a light ray interacts with matter, the light ray changes in some way. Light travels in a straight line until it encounters matter. When a light ray comes into contact with matter, it can be reflected, refracted, or absorbed.
• All objects, regardless of their properties, interact with light in some way.
• The properties of the material light reflects off of affect how we see the object.
• Materials can be transparent, translucent, or opaque depending on what happens to light when it hits them.
• Engineers can apply scientific knowledge about how light moves to design different technologies that solve problems.
• People use different technologies using light to solve a variety of problems.

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## Science Essential Questions

• How is a light ray’s path different when it travels through a vacuum than when it interacts with matter?
• What evidence exists for light being reflected from an object?
• How is absorption different from either refraction or reflection?
• When an incident ray of light interacts with a smooth, reflective material, how can we predict where the reflected ray will be?
• How does the law of reflection explain why we see our image in a mirror?
• How do materials with rougher surfaces reflect light differently from mirrors and other smooth surfaces?
• How do windows increase the amount of natural light that reaches inside a building?
• Why are shadows evidence that a material is opaque ?
• How are transparent materials different from translucent materials?
• What technologies redirect light to solve a specific problem?
• How do periscopes use mirrors to redirect light?

## Common Science Misconceptions

Misconception: Light can move in curves around objects and doesn’t always travel in a straight line.
Fact: Light always moves in a straight line. When it interacts with matter, the matter can redirect the light rays.
Misconception: Light is not in motion.
Fact: Light is in motion. It travels at a constant speed from a source.
Misconception: Light only reflects from mirrors and shiny objects.
Fact: Almost all objects reflect light. This reflected light moves into our eyes, which is how we see.

## Science Vocabulary

Light : a form of kinetic energy that travels through space

Opaque :  a material that blocks all light

Refraction :  occurs when a ray of light passes from one medium to another but changes direction

Sight :  the sense that uses the eyes to take in light information about an object’s position, shape, and color

Transparent :  a material that light passes through completely

Translucent :  a material that some, but not all, light passes through

## Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Designing a Library

When most people think of libraries, they think of books. But for Daniel Heuberger, a public library needs more than books. It also needs to draw people in and make them feel comfortable inside.

Daniel is an architect who helped to design the Bronx Library Center. This library is in the Bronx in New York City. Daniel and his team had two goals with their design. They wanted to make the building feel open and accessible to people on the outside. And they wanted to maximize the natural daylight on the inside.

What is Light?

All light is a form of kinetic energy that travels through space. All light has a source. The sun is the largest source of light on Earth. The sun’s energy travels through space to Earth. When it reaches Earth’s surface, it is absorbed by the planet and changed into heat. When it is absorbed by plants, it is changed into chemical energy through photosynthesis. Ceiling lights, lamps, and flashlights are also sources of light.

Light is complex, and there is still much that scientists don’t know about it. There are different models of light that scientists use to better understand how light moves and how it interacts with matter.

One model is a wave model. This is because in many instances, light behaves in a similar way to sound or water waves. Another model is a ray model. This is the model explored in this unit. This model describes how light moves in a straight line. These straight-line paths are called light rays. Whenever you see a narrow beam of light, it is actually a bundle of many parallel light rays. The ray model is useful for exploring how light interacts with different materials.

Light and Matter

Whenever a light ray interacts with matter, the light ray changes in some way. When a light ray comes into contact with matter, it can be reflected, refracted, or absorbed.

Reflection occurs when a light ray bounces off of the surface of an object. Refraction occurs when a light ray passes from one medium to another and changes its direction. Unlike reflection, the light ray moves through the second material when it refracts. However, the direction of its path changes. Refraction is what happens when you look at an object that is partly in water and partly in air. The object appears bent at the water’s surface because the light rays move in a different direction through the water than through the air.

When a light ray is absorbed by an object, the light energy turns into heat. Dark-colored objects absorb more light than light-colored objects. This is why they warm up faster.

## Hands-on Science Activity

In this lesson, students use what they know about light phenomena to figure out how to engineer a hand-held device that uses mirrors to redirect light so a viewer can see in front of and above their head. Students identify the criteria and constraints of the problem before they design a prototype solution to the problem, given the available materials. Students collect and analyze data on whether they can read the text on the bookshelf template with their prototypes.

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• Concept Map Assessment
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