Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Quick Summary
Light is part of Term 2 in Class 8 Science. This chapter covers the nature of light, laws of reflection, types of mirrors and lenses, and refraction. Understanding these concepts is important for both board exams and for everyday phenomena like rainbows and mirrors.
Key Definitions
- Light: A form of energy that enables us to see objects.
- Ray of light: The path along which light travels, represented by a straight line with an arrow.
- Reflection: The bouncing back of light when it hits a surface.
- Refraction: The bending of light when it passes from one medium to another.
- Angle of incidence: The angle between the incident ray and the normal at the point of incidence.
- Angle of reflection: The angle between the reflected ray and the normal at the point of reflection.
- Normal: A line perpendicular to the reflecting surface at the point of incidence.
- Focal length: The distance between the mirror/lens and its focal point.
Laws of Reflection
1. The angle of incidence = the angle of reflection (∠i = ∠r). 2. The incident ray, the normal, and the reflected ray all lie in the same plane.
Types of Mirrors
| Mirror Type | Shape | Image Type | Uses |
|---|---|---|---|
| Plane mirror | Flat | Virtual, erect, same size | Looking glass, periscope |
| Concave mirror | Curved inward | Real/virtual depending on position | Torch, dental mirror, solar cooker |
| Convex mirror | Curved outward | Virtual, erect, diminished | Rear-view mirror, shop security mirrors |
Refraction of Light
- Light bends when passing from a less dense to a more dense medium.
- It bends towards the normal when entering a denser medium.
- It bends away from the normal when entering a less dense medium.
- Laws of refraction: angle of incidence and angle of refraction are related by Snell's Law.
Types of Lenses
| Lens Type | Shape | Effect on Light | Uses |
|---|---|---|---|
| Convex lens | Thicker at centre | Converges light | Magnifying glass, camera, eye |
| Concave lens | Thinner at centre | Diverges light | Correcting short-sightedness |
Dispersion of Light
- White light splits into seven colours when passed through a prism.
- VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red.
- A rainbow is formed by dispersion of sunlight through water droplets.
Important Questions
One Mark
- State the first law of reflection.
- What type of image is formed by a plane mirror?
- Name the phenomenon that causes a rainbow.
- What is the focal length of a mirror?
- Which mirror is used as a rear-view mirror in vehicles?
Short Answer (3 marks)
- Distinguish between reflection and refraction with one example each.
- Describe the differences between concave and convex mirrors with their uses.
- Explain dispersion of light with the help of a prism diagram.
Long Answer (5 marks)
- State the laws of reflection. Draw a diagram showing reflection of a ray of light from a plane mirror. Explain image formation in a plane mirror.
- Explain the different types of lenses. Draw diagrams showing converging and diverging lenses. Give two uses of each type.
Common Mistakes
- Drawing the normal on the surface instead of perpendicular to it.
- Confusing concave and convex lenses.
- Writing angle of incidence incorrectly (must be measured from the normal, not the surface).
Revision Checklist
- [ ] Textbook reading completed
- [ ] Laws of reflection memorised
- [ ] Mirror and lens diagrams drawn in notebook
- [ ] VIBGYOR colours in correct order
- [ ] Important questions answered in notebook
Frequently Asked Questions
1. The angle of incidence equals the angle of reflection. 2. The incident ray, normal, and reflected ray all lie in the same plane.