CBSE Class 7 Science
Question 14 of 17
Light Shadows and Reflections — Question 14
Back to all questions 14
Question Measure the length of your shadow at 9 AM, 12 PM, and 4 PM with the help of your friend. Write down your observations:
(i) At which of the given times is your shadow the shortest?
(ii) Why do you think this happens?
(i) The shadow will be shortest at 12 PM when the Sun is directly overhead.
(ii) This happens because, at 12 PM, the Sun is at its highest point in the sky, so the angle between the Sun and the ground is almost 90 degrees, casting a shorter shadow.
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