Objects that reflect or refract light may form images. An image is a copy of an object that is formed by reflected or refracted light. According to the law of reflection, light is reflected at the same angle that it strikes a reflective surface. Mirrors reflect all of the light that strikes them and form images. Mirrors include plane (flat), concave, and convex mirrors. Each type of mirror forms images differently. Refraction of light occurs when light passes from one medium to another at an angle other than 90° and the speed of light changes in the new medium. Lenses refract light and form images. Lenses may be concave or convex, and the two types form images differently. Mirrors and lenses are used in optical instruments such as microscopes and telescopes to reflect or refract light and form images.
- MCR.6-8.SCI.9.8; MCR.6-8.TECH.6
- AAAS.6-8.4.F.7; AAAS.6-8.8.D.2; AAAS.6-8.12.D.4
- Outline how light is reflected.
- Describe how mirrors reflect light and form images.
- Explain the refraction of light.
- Describe how lenses refract light and form images.
- Explain how mirrors and lenses are used in optical instruments.
concave: curving inward like the inside of a bowl
convex: curving outward like the outside of a bowl
image: copy of an object that is formed by reflected or refracted light
laser: device that produces a very focused beam of light of just one wavelength and color
law of reflection: law stating that the angle at which reflected rays of light bounce off a surface is equal to the angle at which the incident rays strike the surface
lens: transparent object with one or two curved surfaces that forms images by refracting light
optics: study of visible light and the ways it can be used to extend human vision and do other tasks
Introducing the Lesson
Show students common examples of concave mirrors (such as a makeup mirror and a dental mirror) and convex lenses (such as a hand lens and reading glasses). Pass the items around the room so students have a chance to observe how they affect the appearance of objects. Tell students they will learn in this lesson how mirrors and lenses such as these focus light and extend human vision.
Building Science Skills
Have students do the activity at the URL below. In the activity, they will explore different types of lenses. For each type, they will observe how objects look through the lenses and what happens to light that shines through the lenses. From their observations, they will develop descriptive statements and questions about lenses.
The module at the first URL below was created specifically for use with the PhET simulation “Geometric Optics” (second URL below), and it teaches students about convex lenses. The module includes a lesson plan for teachers, step-by-step directions for students, and a set of Power Point questions for use as warm-up questions or informal assessment.
Assign the two quick, interactive animations below. The first animation shows how the image created by a convex lens is affected by the distance between the object and lens. The second animation shows how various objects look when viewed under a microscope at different magnifications.
Make sure students have a chance to handle and use different types of mirrors and lenses so they can observe the images they create and how the distance of objects from the mirrors or lenses affects the images. It may also be helpful for students to create a compare/contrast table for concave and convex mirrors and lenses to help them sort out their similarities and differences.
A fun extension project is to explore funhouse mirrors, which consist of a combination of concave and convex surfaces. Direct students to the activity at the following URL to apply their knowledge of concave and convex mirrors to funhouse mirrors. Urge them to share what they learn with the class.
Use the inquiry activity at the following URL to help students understand the law of reflection. The only materials required are a mirror, paper, and masking tape. The Web page also includes a Java simulation on angles of reflection.
Make sure students understand that plane mirrors only appear to reverse left and right. It is our brain that interprets the image that way. For a detailed explanation and ways to discourage the misconception that mirrors actually reverse left and right, read the article at this URL: http://scienceinquirer.wikispaces.com/file/view/MirrorReverses.pdf.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook®.
Check students’ mastery of the lesson with Lesson 22.2 Quiz in CK-12 Physical Science for Middle School Quizzes and Tests.
Points to Consider
In this lesson, you read how convex and concave lenses refract light. The human eye, which you can read about in the next lesson “Vision,” also contains a lens.
- How do you think the lens in the eye works? What is its role in vision?
- Do you think the lens in the eye is a concave lens or a convex lens?