CBSE Class 7 Science
Question 8 of 17
Light Shadows and Reflections — Question 8
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Question Sahil, Rekha, Patrick, and Qasima are trying to observe the candle flame through the pipe as shown in Fig. 11.16. Who can see the flame?
Only Rekha can see the flame of the candle because light travels in a straight line, and Rekha’s line of sight is aligned with the flame. The others cannot see the flame because they are not in the path of the pipe where the flame is visible
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