1 Geometrical Optics Pt 1

Light & Optics Unit Becky McCoy

Lesson Title: Geometrical Optics Part 1 Timing: 50 Minutes Target Audience: High School Conceptual Physics Course (9th – 12th grade)

Objectives: Students Will Be Able To: • Identify how light travels. • Describe how light interacts with a mirror through words and diagrams. The Teacher Will Be Able To: • Identify student misconceptions and prior knowledge. • Expose students to the idea of reflection. • Help students to discover everyday occurrences of reflection.

Standards Assessed: New York State, The Physical Setting 4.3 viii. draw ray diagrams to represent the reflection and refraction of waves

Misconception(s) Addressed: • • • •

Light just is and has no origin. Light does not travel. Light does not bounce or reflect. Images stay on the surface of a mirror.

Prior Knowledge: Basic, everyday knowledge of light and optics. Aim: Determine the properties of light and how it travels. Concept Map Vocabulary: • •

Ray model of light Reflection

Necessary Preparation: COPIES • Mirror, Mirror Worksheets • Mirror, Mirror Homework MATERIALS • Cut 2 squares of cardboard. In one square cut one slit in the middle and in the other square cut two slits. Have tape available to attach the cardboard squares to the flashlight. • Punch a hole on the side of the soda can, near the bottom. Be sure the sharp edges are on the inside of the can.

Light & Optics Unit Becky McCoy • Computer and projector. • Small mirrors. • Masking tape. SET UP • Physics Push-Up Demonstration

Light & Optics Unit Becky McCoy

Lesson Plan

Aim: Determine the properties of light and how it travels. Physics Push-Up: Light Brainstorm (10 minutes) Have students take five minutes describe how light travels on a piece of paper. Does it travel straight or can it bend? Draw a light source and how the light travels from it. Materials: • Flashlight • Cardboard square with 1 slit • Cardboard square with 2 slits • Empty soda can with hole near bottom • Water to fill the can Procedure: 5 minutes 1. Shine the flashlight against a blank wall. 2. Attach the one slit square to the flashlight and shine it against the same spot. 3. Attach the two slit square to the flashlight and shine it against the wall. 4. Holding one finger over the hole in the soda can, fill the can with water. Holding the can above a sink or bucket, shine a flashlight down into the can, and let go of the hole. Questions to Ask: • What do you observe when the flashlight shine against the wall? • What is different when the one slit cardboard square shines on the wall? • What about the two slit cardboard square? • Why does the light seem to bend out of the can? How can you explain this?

Activity: Mirror, Mirror (15 minutes) Transition by describing how light reflects off the water and the inside of the can. An obvious example of reflection would be a mirror. Today’s activity will explore how mirrors work and ways we diagram how light travels. Materials: • Small mirrors, one for every partnership in the classroom. • Masking tape. • Worksheets. Procedure: 1. Find a place where there is a wall with plenty of space around it. Attach the mirror at eye level on a wall with masking tape. Cover the mirror with a piece of paper.

Light & Optics Unit Becky McCoy 2. Guess where you and your partner need to stand to see each other's reflection on the mirror. When you both agree on the places, mark them on the floor with 6-inch pieces of masking tape and draw a diagram on your worksheet. 3. Remove the paper from the mirror. Stand at your chosen place to determine if you can see each other in the mirror. 4. Try different spots until you can see your partner. Mark the places that work with the 6-inch pieces of masking tape and draw a new diagram. 5. Place long pieces of masking tape on the floor from the center of your 6-inch place markers to the wall straight under the center of the mirror. These should be straight lines. 6. Look at the angles made by the taped lines on the floor and the wall to see if they are the same size. Remember that light bounces off a mirror at the same angle that it arrives. Therefore, when the light from your face travels to the mirror on the wall, it should bounce off the mirror at the same angle to the eyes of your partner. 7. On your worksheet, write a description of what you did in this activity. Include a diagram with lines showing how light reflects off a mirror. Questions to Ask: • What happened? • Were you surprised? • How does this affect your perception of light? • How can you describe how light travels from the results of this activity? • What do you hope to investigate more with regards to light?

Activity Summary: Geometrical Optics Power Point (15 minutes) Referring to the first third of the Geometrical Optics Power Point, ask students to help draw ray diagrams of light interacting with a mirror. Ideally, this would be done with a SMART Board or projected on a white board, so you can draw in lines. Take time for the information to sink in and answer students’ questions.

Homework: Mirror, Mirror, cont. (5 minutes) See Mirror, Mirror Homework

Exit Strategy: 321 Exit Cards (5 minutes) 3 examples of reflection, other than what we discussed in class (the water in the soda can and mirrors). 2 properties of light. 1 thing you learned.

Extension Activity: Extra ray diagrams on the board and/or discussions of experiences of reflection.

Light & Optics Unit Becky McCoy

Assessment: • • • • •

321 Exit Cards Mirror, Mirror Worksheets Mirror, Mirror Homework Teacher circulating room during activity Teacher evaluation of students responses/questions throughout lesson

Resources: Bill Nye Website: http://www.billnye.com Making Sense of Secondary Science by Rosalind Driver Molecular Expressions: http://micro.magnet.fsu.edu/optics/activities/students/mirror.html University of Dallas: http://phys.udallas.edu/C3P/Preconceptions.pdf University of Virginia: http://galileo.phys.virginia.edu/classes/620/Optics_Activities.html

Notes & Adaptations:

Light & Optics Unit Becky McCoy Name ___________________________________________ Date _______________

Mirror, Mirror Worksheet Procedure: 1. Find a place where there is a wall with plenty of space around it. Attach the mirror at eye level on a wall with masking tape. Cover the mirror with a piece of paper. 2. Guess where you and your partner need to stand to see each other's reflection on the mirror. When you both agree on the places, mark them on the floor with 6-inch pieces of masking tape and draw a diagram on your worksheet. 3. Remove the paper from the mirror. Stand at your chosen place to determine if you can see each other in the mirror. 4. Try different spots until you can see your partner. Mark the places that work with the 6-inch pieces of masking tape and draw a new diagram. 5. Place long pieces of masking tape on the floor from the center of your 6-inch place markers to the wall straight under the center of the mirror. These should be straight lines. 6. Look at the angles made by the taped lines on the floor and the wall to see if they are the same size. Remember that light bounces off a mirror at the same angle that it arrives. Therefore, when the light from your face travels to the mirror on the wall, it should bounce off the mirror at the same angle to the eyes of your partner. 7. On your worksheet, write a description of what you did in this activity. Include a diagram with lines showing how light reflects off a mirror. Diagrams:

Light & Optics Unit Becky McCoy Name _____________________________________________ Date ______________

Mirror, Mirror Homework Directions: Find a mirror hanging on a wall. Take a picture or draw what you see in the mirror below (you can email me the picture). Make a ray diagram of what you see, including the mirror, all objects seen in the reflection, and yourself. Don’t forget to include light sources!!