CBSE Class 7 Science
Question 13 of 17
Light Shadows and Reflections — Question 13
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Question Write your name on a piece of paper and hold it in front of a plane mirror such that the paper is parallel to the mirror. Sketch the image. What difference do you notice? Explain the reason for the difference.
When you look at the paper through the plane mirror, the image will be laterally inverted (flipped horizontally). You will notice that the letters of your name appear backward, as the mirror reverses left and right.
Chapter 11: Light
Reflection follows two laws: angle of incidence equals angle of reflection, and all rays are in the same plane. Plane mirror images are virtual, erect, same size, and laterally inverted. Concave mirrors converge light (used in torches, dentist mirrors). Convex mirrors diverge light (used in rear-view mirrors). Dispersion splits white light into VIBGYOR through a prism. Rainbows are natural dispersion by water droplets.
Theme: Physics | Difficulty: Age-appropriate for Class VII
Key Formulas & Equations
| Formula / Equation | When to Use |
|---|---|
| Law 1: Angle of incidence = Angle of reflection (∠i = ∠r) | First law of reflection |
| VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red | Spectrum colours in order |
Must-Know Concepts
- Two laws of reflection: ∠i = ∠r; same plane
- Plane mirror: virtual, erect, same size, laterally inverted, equal distance behind
- Lateral inversion: left-right swap (AMBULANCE written in reverse)
- Concave mirror: converges light, uses = torch, headlight, dentist, solar cooker
- Convex mirror: diverges light, wider view, uses = rear-view mirror
- Real image: on screen; Virtual image: cannot be on screen
- Dispersion: white light through prism gives VIBGYOR spectrum
Common Mistakes to Avoid
- Thinking plane mirror image is real — it is virtual
- Confusing lateral inversion with upside-down
- Thinking white light is pure — it is a mixture of 7 colours
Scoring Tips
- Draw ray diagrams with incident ray, normal, reflected ray, and angles
- List 5 properties of plane mirror image
- Compare concave and convex mirrors with uses