Light
Focused last-minute revision notes with clear concepts, exam traps, key comparisons and compact practice.
Chapter Snapshot
- We see objects when light from them or reflected by them enters our eyes.
- Reflection follows two laws: angle of incidence equals angle of reflection, and incident ray, reflected ray and normal lie in one plane.
- Smooth surfaces give regular reflection; rough surfaces give diffused reflection.
- Diffused reflection still obeys the laws of reflection at each point.
- Multiple reflections produce repeated images and are used in periscopes and kaleidoscopes.
- The human eye includes cornea, iris, pupil, lens, retina and optic nerve.
- The iris controls pupil size and therefore light entering the eye.
- The retina contains light-sensitive cells and sends signals through the optic nerve.
- Good lighting, eye hygiene and professional care protect vision.
- Braille is a raised-dot reading and writing system used by many visually impaired people.
What You Will Learn
- State and apply laws of reflection
- Differentiate regular and diffused reflection
- Explain multiple images
- Identify major parts of human eye
- Explain basic image formation on retina
- Describe eye care
- Explain Braille at basic level
Last-Minute Chapter Map
Reflection follows precise geometry, while the human eye receives and focuses reflected light to form visual signals.
1. Reflection
When light strikes a surface and returns into the same medium, it is reflected. The incoming path is the incident ray, the outgoing path the reflected ray, and the perpendicular at the point of incidence is the normal.
2. Laws of Reflection
The angle of incidence is measured between incident ray and normal; the angle of reflection between reflected ray and normal. The laws are: (1) angle of incidence equals angle of reflection; (2) incident ray, reflected ray and normal lie in the same plane.
3. Regular and Diffused Reflection
A smooth surface sends parallel incident rays in orderly directions and can form a clear image: regular reflection. A rough surface has differently oriented tiny surfaces, so reflected rays scatter: diffused reflection. Each small reflection still obeys the laws.
4. Multiple Reflection
Light can reflect more than once. Two mirrors can form multiple images. Periscopes redirect light using repeated reflection; kaleidoscopes use repeated reflections to create symmetrical patterns.
5. Human Eye
Light enters through the cornea and pupil. The iris controls pupil size. The lens focuses light onto the retina, which contains light-sensitive cells. Signals travel through the optic nerve to the brain.
6. Care of the Eyes
Read in suitable light, maintain appropriate viewing distance, avoid staring at intense light, keep screens at comfortable brightness and obtain professional eye checks when needed. Vitamin A deficiency can impair vision, but supplements should be taken only as medically advised.
7. Braille
Braille uses patterns of raised dots that are read by touch. It enables reading and writing for many people who are blind or have severe visual impairment.
Regular vs Diffused Reflection
| Feature | Regular Reflection | Diffused Reflection |
|---|---|---|
| Surface | Smooth | Rough |
| Reflected rays | Remain orderly | Scatter in many directions |
| Clear image | Usually possible | Usually not |
| Laws of reflection | Obeyed | Obeyed locally |
Essential Formula
Law of Reflection
i = angle of incidence, r = angle of reflection; both measured from the normal
Exam Focus
Must Revise Before the Exam
- Incident ray/reflected ray/normal
- Laws of reflection
- Regular vs diffused
- Multiple images
- Periscope/kaleidoscope
- Eye parts
- Retina/optic nerve
- Eye care
- Braille
Common Mistakes
Key Terms
Key Terms
Quick Revision
Quick Revision
- Angle of incidence = angle of reflection.
- Angles are measured from normal.
- Incident ray, reflected ray and normal lie in one plane.
- Regular reflection from smooth surfaces can form clear images.
- Diffused reflection comes from rough surfaces.
- Eye: cornea → pupil → lens → retina → optic nerve.
- Iris controls pupil size.
- Braille uses raised dots read by touch.
Practice Questions
The angle of incidence is measured from the:
A. mirror surface
B. normal
C. reflected ray only
D. eye
View Solution
Correct Answer: B. normal
Angles in reflection are measured from the normal.
A clear image is usually formed by:
A. regular reflection
B. diffused reflection
C. absorption only
D. sound
View Solution
Correct Answer: A. regular reflection
Smooth surfaces produce orderly regular reflection.
Which part controls the amount of light entering the eye?
A. iris
B. retina
C. optic nerve
D. eyelid only
View Solution
Correct Answer: A. iris
The iris adjusts pupil size.
Braille is read mainly by:
A. hearing
B. touch
C. smell
D. taste
View Solution
Correct Answer: B. touch
Braille uses raised dot patterns felt by touch.
State the two laws of reflection.
View Solution
Angle of incidence equals angle of reflection, and the incident ray, reflected ray and normal all lie in the same plane.
Why does a rough wall not form a clear image although it reflects light?
View Solution
Different tiny surface orientations reflect light in many directions, producing diffused reflection instead of an orderly image.
If a ray strikes a mirror at 35° to the normal, what is the reflection angle?
View Solution
By the law of reflection, the angle of reflection is also 35°.
Chapter Summary
Chapter Summary
- Angle of incidence = angle of reflection.
- Angles are measured from normal.
- Incident ray, reflected ray and normal lie in one plane.
- Regular reflection from smooth surfaces can form clear images.
- Diffused reflection comes from rough surfaces.
- Eye: cornea → pupil → lens → retina → optic nerve.
- Iris controls pupil size.
- Braille uses raised dots read by touch.