Materials Needed

• Flat (plane) mirror
• Highly polished metal spoon (functions as both concave and convex mirrors)
• Double convex lens and double concave lens (magnifying glass works for convex)
• Red laser pointer or focused LED flashlight
• Clear glass rectangular container filled with water (add a drop of milk to make the laser beam visible)
• Sheet of white paper or cardstock
• Ruler and protractor
• Pencil and colored pens/markers
• Comb and tape (to create parallel light rays from a flashlight, if lasers are unavailable)
• Printout: Ray Diagram Quick Guides (included in activity setup)

Lesson Overview & Objectives

In this lesson, you will explore how light behaves when it bounces off surfaces (reflection) and when it passes through transparent materials (refraction). Through hands-on experimentation with mirrors and lenses, you will discover why your reflection flips upside down in a spoon, how magnifying glasses work, and how engineers use optics to build telescopes, cameras, and glasses.

Learning Objectives

• Objective 1: Demonstrate and explain the Law of Reflection using plane, concave, and convex mirrors.
• Objective 2: Compare how light bends (refracts) when passing through concave versus convex lenses.
• Objective 3: Draw accurate ray diagrams to predict whether an image will be real or virtual, upright or inverted, and magnified or diminished.
• Objective 4: Apply knowledge of optics to solve a practical "light maze" engineering challenge.

Success Criteria

• I can state the Law of Reflection and accurately measure angles of incidence and reflection.
• I can identify whether a mirror or lens is concave or convex based on its shape and how it affects light rays.
• I can trace light rays to locate the focal point ($F$) of curved optics.
• I can explain at least two real-world technology applications for both curved mirrors and lenses.

1. Introduction: Hook & Objectives (10 Minutes)

The Spoon Mystery & Broken Pencil Trick

Interactive Hook: Grab a highly polished metal spoon and look at your reflection on the inside (bowl) of the spoon. What do you notice? You're upside down! Now, flip the spoon over and look at the back side. You're right-side up, but your nose looks gigantic! Next, drop a pencil into a glass half-filled with water. Look at it from the side. Why does the pencil look broken or shifted?

Talking Points for Educator / Discussion Prompts:

• "Light travels in straight lines at roughly 300,000 kilometers per second in a vacuum. But when it hits an obstacle or changes medium, its speed and direction change."
• "The spoon acts as two different types of curved mirrors: concave (curved inward like a cave) and convex (curved outward like a dome). Different shapes force light rays to do very different things."
• "The pencil looks broken because light slows down when moving from air into water, causing the light waves to bend. This bending is called refraction."

2. Body: Content & Guided Practice (40 Minutes)

Part A: Reflection & Mirrors (I Do / We Do)

1. The Law of Reflection (Plane Mirrors)

Concept: When a light ray hits a flat mirror, it bounces off at the exact same angle it hit. The angle of incidence ($\theta_i$) equals the angle of reflection ($\theta_r$). Angles are always measured relative to the normal line (an imaginary line perpendicular to the surface).

2. Curved Mirrors (Concave vs. Convex)

• Concave Mirrors (Converging): Curve inward. They collect parallel light rays and focus them down to a single spot called the Focal Point ($F$). If you stand far away, your image is inverted (upside down). If you get closer than the focal point, your image suddenly flips right-side up and becomes huge! (Examples: Makeup mirrors, satellite dishes, headlight reflectors).
• Convex Mirrors (Diverging): Curve outward. They spread light rays apart. They always form upright, smaller images, but they give you a wide-angle view. (Examples: Store security mirrors, passenger side car mirrors - "Objects in mirror are closer than they appear").

Part B: Refraction & Lenses (I Do / We Do)

1. Refraction: Light Speed Shift

Concept: Refraction happens because light changes speed when moving from one transparent material to another (e.g., from air into glass or water). When light slows down, it bends toward the normal line. When it speeds up, it bends away from the normal line.

2. Lenses (Convex vs. Concave)

Lenses use refraction to bend light predictably because they have curved glass/plastic surfaces.

• Convex Lens (Converging Lens): Thicker in the middle, thinner at the edges. Parallel light rays passing through are bent inward toward a focal point.
  Key Uses: Magnifying glasses, hyperopia (farsightedness) correction, camera lenses, human eye lens.
• Concave Lens (Diverging Lens): Thinner in the middle, thicker at the edges. Parallel light rays passing through are bent outward, spreading apart as if coming from a virtual focal point behind the lens.
  Key Uses: Myopia (nearsightedness) correction, peepholes in doors, laser beam expanders.

Part C: Independent Hands-On Lab (You Do)

3. Conclusion: Review & Assessment (10 Minutes)

Lesson Summary & Recap

• Reflection is the bouncing of light off a surface. The angle in equals the angle out ($\theta_i = \theta_r$).
• Refraction is the bending of light caused by a change in speed when entering a new medium.
• Concave Mirrors & Convex Lenses are converging systems—they bring light rays together at a focal point.
• Convex Mirrors & Concave Lenses are diverging systems—they spread light rays apart.

Formative / Summative Assessment Questions

1. Concept Check: If you are nearsighted (you can see close up, but distant objects are blurry because your eye focuses light in front of your retina), do you need concave or convex lenses in your glasses to fix it? Why?
   (Answer: Concave lenses, because they diverge/spread out the rays slightly before they enter the eye, pushing the focal point back onto the retina).
2. Ray Diagram Challenge: What happens to an image formed by a concave mirror when you move an object closer than the focal point?
   (Answer: The image flips from inverted/real to virtual, upright, and magnified).
3. Real-World Application: Why do rear-view side mirrors on cars use convex mirrors instead of flat plane mirrors?
   (Answer: Convex mirrors provide a wider field of view, helping eliminate blind spots, even though objects appear smaller/further away).

Differentiation & Adaptations

For Struggling Learners / Scaffolding

• Use physical color-coded strings (e.g., red for incident ray, blue for reflected ray) taped to the table to visualize light paths before drawing them.
• Provide pre-drawn ray diagram grids where the student only needs to connect dots to find the focal point.
• Focus on qualitative descriptions (up/down, big/small) before introducing quantitative protractor measurements.

For Advanced Learners / Extensions

• Quantitative Challenge: Introduce the Lens/Mirror Equation: $\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}$ (where $f$ is focal length, $d_o$ is object distance, and $d_i$ is image distance). Calculate exact image positions mathematically and verify them with physical lenses.
• Snell's Law: Calculate the refractive index ($n$) of water using Snell's Law ($n_1 \sin\theta_1 = n_2 \sin\theta_2$) based on measured angles with a protractor.
• Telescope Construction: Challenge Heidi to align two convex lenses of different focal lengths in a paper tube to create a working Keplerian refracting telescope!