TEACHGYAN • CLASS 7 SCIENCE • CURIOSITY
Chapter 11 — Light: Shadows and Reflections
Light • Shadows • Reflection • Mirrors • Ray Diagrams
🌟 Chapter at a Glance
Light enables us to see objects. When light encounters an object, it may be transmitted, absorbed or reflected. Shadows form when an opaque object blocks light from a source.
💡 1. Sources of Light
Objects that emit their own light are luminous, such as the Sun and a flame. Objects that do not produce light but are visible because they reflect light are non-luminous.
🌑 2. How Shadows Form
A shadow forms when an opaque object comes between a light source and a screen. The shadow gives information about the path of light and the position of the object.
| Material | Effect on light |
|---|---|
| Transparent | Allows most light through |
| Translucent | Allows some light through and scatters it |
| Opaque | Blocks light |
🪞 3. Reflection
Reflection is the return of light from a surface. Smooth, polished surfaces can produce clear reflections; rough surfaces scatter reflected light in many directions.
📐 4. Plane Mirror
A plane mirror forms an upright image. The image is virtual and appears behind the mirror. The image is laterally inverted, meaning left and right appear reversed.
🔦 5. Investigating Light
- Use a torch or other safe light source.
- Place an opaque object between the source and a screen.
- Change the object-source distance and observe the shadow.
- Record observations rather than relying only on memory.
🧠 Worked Examples
- Why does a wall become visible? Light falls on it and is reflected toward our eyes.
- Why does an opaque object form a shadow? It blocks light from reaching the screen.
- Why does a rough surface usually not form a clear image? It scatters reflected light in many directions.
🧩 Interactive MCQs
- A shadow needs a light source, an opaque object and: A a screen/surface B only water C a magnet D a battery
- A plane mirror forms an image that is generally: A upright and virtual B upside down and real C always coloured D absent
- A material that blocks most light is: A opaque B transparent C translucent D luminous
- Reflection from a smooth mirror is relatively: A regular B random only C absent D thermal
Answers: 1-A, 2-A, 3-A, 4-A
📌 Case-Based Learning — Shadow Theatre
A student moves a cardboard figure closer to a lamp while keeping the screen in place.
- What happens to the shadow size when the object moves closer to the lamp?
- Why does the shadow form?
- How could the student make a fair comparison?
- What variables should be recorded?
🔥 HOTS / Competition Corner
- Why can the same object produce shadows of different sizes?
- Design an investigation to study how changing the light-source distance affects shadow size.
- Explain why we can see a book even though the book is not luminous.
📝 Five-Level Worksheet
| Level | Task |
|---|---|
| 1 | Define luminous, opaque, shadow and reflection. |
| 2 | Classify materials by their interaction with light. |
| 3 | Predict shadow changes in different arrangements. |
| 4 | Interpret a mirror or shadow investigation. |
| 5 | Design a shadow-theatre experiment and justify variables. |
🏆 Mastery Checklist
- ☐ I can explain how shadows form.
- ☐ I can classify materials as transparent, translucent or opaque.
- ☐ I can explain reflection.
- ☐ I can describe the image formed by a plane mirror.
- ☐ I can design a fair light investigation.
🔁 One-Minute Revision
Light allows vision; opaque objects can form shadows; reflection is the return of light from a surface. A plane mirror produces an upright, virtual and laterally inverted image.