Bihar Board Class 10 · Science · Matric exam 2027
Chapter 11: The Human Eye and the Colourful World — notes
The chapter’s 7 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. The Human Eye - How We See
Okay, so, your eye works much like a camera.
- • Light path: Cornea -> Pupil (size set by Iris) -> Eye lens -> Retina
- • Retina: light-sensitive cells generate electrical signals
- • Signals travel via Optic nerve to the Brain
- • Bright light: iris contracts pupil (less light in)
- • Dim light: iris expands pupil (more light in)
2. Power of Accommodation
Okay, so let's see how your eye focuses on both near and far things.
- • Accommodation = ability of eye lens to adjust focal length
- • Ciliary muscles relax -> lens thin -> focal length increases -> far objects clear
- • Ciliary muscles contract -> lens thick -> focal length decreases -> near objects clear
- • Near point (least distance of distinct vision) = about 25 cm
- • Far point of normal eye = infinity
3. Defects of Vision and Their Correction
Okay, so sometimes the eye loses its power of accommodation.
- • Myopia: sees near, not far; image forms in front of retina; corrected by CONCAVE lens
- • Hypermetropia: sees far, not near; image forms behind retina; corrected by CONVEX lens
- • Presbyopia: near point recedes with age due to weak ciliary muscles
- • Bifocal lens: upper concave (distant), lower convex (near)
4. Refraction Through a Prism
Okay, so let's think about a prism now.
- • Prism: two triangular bases, three rectangular lateral surfaces
- • Angle of prism = angle between the two lateral faces
- • PE (incident) -> EF (refracted, bends toward normal, air to glass)
- • EF -> FS (emergent, bends away from normal, glass to air)
- • Angle of deviation = angle D, between incident ray and emergent ray
5. Dispersion of White Light
Okay, so let's talk about sunlight and a prism.
- • Dispersion = splitting of white light into component colours
- • Colour order: VIBGYOR (Violet,Indigo,Blue,Green,Yellow,Orange,Red)
- • Red bends least, Violet bends most
- • Spectrum = band of coloured components of light
- • Rainbow = natural spectrum from dispersion by water droplets, opposite to Sun
6. Atmospheric Refraction and Twinkling of Stars
Okay, so you've seen how hot air above a fire makes things look shaky.
- • Atmospheric refraction = bending of light by earth's atmosphere
- • Starlight bends towards normal -> apparent position higher than actual
- • Stars = point sources -> light flickers -> twinkling
- • Planets = extended sources -> variations average to zero -> no twinkling
- • Sun visible ~2 min before sunrise and ~2 min after sunset
7. Scattering of Light - Blue Sky and Red Sun
Okay, so — the air around us is full of tiny particles.
- • Tyndall effect: scattering of light by colloidal particles, makes beam path visible
- • Fine particles scatter blue (shorter wavelength) more strongly
- • Red wavelength is about 1.8 × greater than blue wavelength
- • No atmosphere -> no scattering -> sky looks dark
- • Sunrise/sunset: thick atmosphere -> blue scattered away -> Sun looks red
- • Danger signals are red: red is least scattered by fog or smoke
Summary
Okay, so let's look back at everything we covered in this chapter. We started with the human eye, and how the cornea, pupil, iris, eye lens and retina work together with the optic nerve and brain to let you see. Then we talked about accommodation, and about the near point at 25 cm and the far point at infinity. After that came the three refractive defects — myopia, hypermetropia and presbyopia — and how concave or convex lenses correct each one. Next, we looked at refraction through a prism, and that led us into dispersion, where white light splits into the VIBGYOR spectrum, and how rainbows form. Then came atmospheric refraction — this one explains why stars twinkle, why planets shine steadily, and why the Sun seems to rise a little early and set a little late. And finally, scattering of light gave us the Tyndall effect, the blue of a clear sky, and the reddish Sun at sunrise and sunset. That's a lot of ground, isn't it? Tell me — of all these, which idea felt the most surprising to you?
AskMedha · Medha Ma’am — Bihar Board Class 10 Science, Chapter 11. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "The Human Eye and the Colourful World" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
The same preparation, with Medha Ma’am — on your phone
Every question of every chapter with its model answer, practice questions in the board’s own shapes, 60 minutes of class a day, written answers marked, a test every Sunday and a WhatsApp report to parents.
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