Bihar Board Class 10 · Science · Matric exam 2027
Chapter 10: Light – Reflection and Refraction — 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. Why we see things, and light travels straight
Okay, so let's think about why you can see things around you at all.
- • We see objects because they reflect light into our eyes.
- • No light in dark room = nothing visible.
- • Light travels in straight lines = ray of light.
- • Sharp shadow of opaque object proves this.
2. Laws of Reflection and Spherical Mirrors
Okay, so you already know the two laws of reflection.
- • Law 1: angle of incidence = angle of reflection
- • Law 2: incident ray, normal, reflected ray — same plane
- • Concave mirror: curves inward; Convex mirror: curves outward
- • P = pole, C = centre of curvature, R = PC
- • Principal axis: line through P and C
- • R = 2f ; F lies midway between P and C
3. Images by Concave and Convex Mirrors, and Their Uses
Okay, so let's talk about what a concave mirror shows us.
- • Concave mirror: image varies with object position (Table 10.1)
- • Object between P and F: image virtual, erect, enlarged, behind mirror
- • Convex mirror: always virtual, erect, diminished image
- • Concave mirror uses: torches, headlights, shaving mirrors, dentist's mirror
- • Convex mirror use: rear-view mirror (wider field of view)
4. Sign Convention, Mirror Formula and Magnification
Okay, so — now we need a system to find exactly where an image forms, and how big it is.
- • New Cartesian Convention: pole = origin, principal axis = x-axis
- • Distances right of pole: positive; left: negative
- • Mirror formula: 1/v + 1/u = 1/f
- • Magnification m = h'/h = -v/u
- • Example: R=+3.00 m, u=-5.00 m, f=+1.50 m
- • Result: v=+1.15 m, m=+0.23 (virtual, erect, smaller)
5. Refraction of Light and Refractive Index
Okay, so — think about light moving from one transparent medium into another, at an angle.
- • Refraction: light bends on entering another medium (speed changes)
- • Laws: (i) incident ray, refracted ray, normal in same plane
- • (ii) sin i / sin r = constant (Snell's law)
- • Refractive index n = Speed of light in air / Speed of light in medium = c/v
- • Rarer to denser: bends towards normal (slows down)
- • Denser to rarer: bends away from normal (speeds up)
6. Lenses: Convex and Concave, Image Formation
A lens is a transparent material with at least one spherical surface.
- • Lens: transparent material with at least one spherical surface
- • Convex lens: thicker at middle, converges rays (converging lens)
- • Concave lens: thicker at edges, diverges rays (diverging lens)
- • O = optical centre (ray through O: no deviation)
- • Convex lens image varies with object position (Table 10.4)
- • Concave lens: always virtual, erect, diminished image
7. Lens Formula, Magnification and Power of a Lens
Okay, so lenses also have a sign convention.
- • Lens formula: 1/v − 1/u = 1/f
- • Magnification m = h'/h = v/u
- • Example: f=+10 cm, u=-15 cm, h = 2.0 cm
- • Result: v=+30 cm, h'=-4.0 cm, m=-2 (real, inverted)
- • Power P = 1/f, unit dioptre (D), f in metres
- • Net power: P = P1 + P2 + P3 + ...
Summary
Okay, so let's look back at everything we covered. We started by seeing why we can see objects at all — light reflects off them in straight lines into our eyes. That's also why shadows come out sharp. Then we met spherical mirrors, concave and convex, and their parts — pole, centre of curvature, radius of curvature, principal axis, and focal length, with R = 2f. We saw how a concave mirror's image keeps changing as the object moves, while a convex mirror always gives a virtual, erect, diminished image. We also looked at where each one is used in daily life. Using the New Cartesian Sign Convention, we got the mirror formula 1/v + 1/u = 1/f, and magnification m = -v/u — remember the rear-view mirror example? After that came refraction — light bends because it changes speed moving between media. That follows Snell's law, sin i / sin r = constant, and this constant is the refractive index, n = c/v. Finally, we studied convex and concave lenses, how they form images, the lens formula 1/v − 1/u = 1/f, magnification m = v/u, and the power of a lens, P = 1/f, measured in dioptres. So, out of all this, which idea do you think connects mirrors and lenses the most?
AskMedha · Medha Ma’am — Bihar Board Class 10 Science, Chapter 10. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Light – Reflection and Refraction" 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.
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