Is it correct to say: Ignoring sign convention?

Always measure distances from pole/optical centre and take incident ray direction as positive. Concave mirror: f negative. Convex mirror: f positive.

Is it correct to say: Using mirror formula for lens (sign of 1/u)?

Mirror: 1/v + 1/u = 1/f. Lens: 1/v − 1/u = 1/f. The minus sign matters.

Is it correct to say: Reporting refractive index less than 1 for glass or water?

Absolute n = c/v ≥ 1 always. n<1 is possible only between two media (relative n).

Is it correct to say: Confusing power of lens with focal length?

P = 1/f in metres, unit dioptre. A convex lens of f = 25 cm has P = +4 D, not +25.

Is it correct to say: Drawing ray diagrams without labels?

Every ray diagram needs: incident ray, refracted/reflected ray, principal axis, F, C, image position, arrows. Missing labels cost marks.

Is it correct to say: Assuming image is virtual because it is on the same side?

For a mirror, image on same side as object (in front) is REAL; behind mirror is virtual.

Light — Reflection and Refraction

Q: Is it correct to say: Confusing power of lens with focal length?

P = 1/f in metres, unit dioptre. A convex lens of f = 25 cm has P = +4 D, not +25.

Q: Is it correct to say: Drawing ray diagrams without labels?

Every ray diagram needs: incident ray, refracted/reflected ray, principal axis, F, C, image position, arrows. Missing labels cost marks.

Q: Is it correct to say: Assuming image is virtual because it is on the same side?

For a mirror, image on same side as object (in front) is REAL; behind mirror is virtual.

Laws of reflection, refraction, mirror and lens formulas, refractive index — Maharashtra SSC Science-1 Ch 6 & 7

📐 9 formulas✏️ 3 examples🎯 6 practice⚖️ 6 marks🏫 Maharashtra State Board📚 Class 10✓ 2025–26 syllabus

💡

Board Exam Tips

→Ray diagrams — six standard positions for concave mirror & convex lens. Marks depend on labels.
→Sign convention: distances measured from pole/optical centre; incident ray direction is +.
→Mirror formula 1/v + 1/u = 1/f — plug values with correct sign; convex mirror ⇒ f positive, concave ⇒ f negative.
→Snell's law + refractive index + numerical (n = c/v) — regular 3-mark question.
→Distinguish real vs virtual image with a table (position, nature, size).

📊 Diagram

Ray diagram: object beyond C of concave mirror — real, inverted, diminished image

📐 Formulas(9)

Laws of Reflection★ Board fav

∠ i = ∠ r

Mirror Formula★ Board fav

\frac{1}{v} + \frac{1}{u} = \frac{1}{f}

Magnification (Mirror)

m = \frac{h ^{'}}{h} = - \frac{v}{u}

Focal Length and Radius of Curvature

f = \frac{R}{2}

Snell's Law★ Board fav

n_{21} = \frac{s i n i}{s i n r} = \frac{n _{2}}{n _{1}}

Absolute Refractive Index

n = \frac{c}{v}

Symbol	Meaning
$c$	Speed of light in vacuum ≈ 3×10⁸ m/s
$v$	Speed of light in the medium (m/s)

Lens Formula

\frac{1}{v} - \frac{1}{u} = \frac{1}{f}

Power of a Lens

P = \frac{1}{f ( in m )}

Magnification (Lens)

m = \frac{h ^{'}}{h} = \frac{v}{u}

✏️ Solved Examples

1Solved Exampleeasy5 steps

An object is placed 30 cm in front of a concave mirror of focal length 10 cm. Find the position and nature of the image.

Apply sign convention (u negative, f negative for concave)

u = - 30 cm, f = - 10 cm

2Solved Exampleboard3 steps

The refractive index of glass with respect to air is 1.5. Find the speed of light in glass. (c = 3×10⁸ m/s)

Absolute refractive index

n = \frac{c}{v}

3Solved ExampleHOTS5 steps

A convex lens forms a real image three times the size of the object at a distance of 60 cm from the lens. Find the focal length of the lens.

Real image ⇒ v positive (converging lens convention); m = −3

v = + 60 cm, m = \frac{v}{u} = - 3

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Ignoring sign convention
✓Always measure distances from pole/optical centre and take incident ray direction as positive. Concave mirror: f negative. Convex mirror: f positive.
2
Using mirror formula for lens (sign of 1/u)
✓Mirror: 1/v + 1/u = 1/f. Lens: 1/v − 1/u = 1/f. The minus sign matters.
3
Reporting refractive index less than 1 for glass or water
✓Absolute n = c/v ≥ 1 always. n<1 is possible only between two media (relative n).
4
Confusing power of lens with focal length
✓P = 1/f in metres, unit dioptre. A convex lens of f = 25 cm has P = +4 D, not +25.
5
Drawing ray diagrams without labels
✓Every ray diagram needs: incident ray, refracted/reflected ray, principal axis, F, C, image position, arrows. Missing labels cost marks.
6
Assuming image is virtual because it is on the same side
✓For a mirror, image on same side as object (in front) is REAL; behind mirror is virtual.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
State the two laws of reflection of light.
Q2
An object is placed at 20 cm from a convex lens of focal length 10 cm. Find v and m.
Q3
Refractive index of water is 4/3. Find the speed of light in water.
Q4
A concave lens has focal length 25 cm. Find its power.
Q5
State any two uses of a concave mirror.
Q6
An object 5 cm high placed at 30 cm from a convex mirror of f = 15 cm. Find image position and height.

📝 Notes

Light — Reflection and Refraction (Maharashtra SSC)

Maharashtra SSC splits light into two textbook chapters: Reflection of Light (Ch 6 of Science-1) and Refraction / Lenses (Ch 7). This page covers both.

Reflection — types and rules

Regular: on smooth surface (mirror). Clear image.
Diffuse: on rough surface (paper). No image, just brightness.

Both obey the same two laws.

Spherical mirror image table (concave)

| Object position | Image position | Nature | |---|---|---| | At infinity | At F | Real, inverted, highly diminished | | Beyond C | Between F and C | Real, inverted, diminished | | At C | At C | Real, inverted, same size | | Between C and F | Beyond C | Real, inverted, magnified | | At F | At infinity | Real, inverted, highly magnified | | Between F and P | Behind mirror | Virtual, erect, magnified |

Convex mirror always gives virtual, erect, diminished image regardless of object position.

Refraction — bending of light

Light bends when it enters a medium of different optical density:

Denser medium ⇒ ray bends toward normal.
Rarer medium ⇒ ray bends away from normal.

Total internal reflection (SSC favourite)

When light goes from denser to rarer medium at angle greater than the critical angle, all light is reflected back. Applications: mirage, sparkle of diamond, optical fibre.

Lenses — quick rules

Convex (converging) — positive f, positive P.
Concave (diverging) — negative f, negative P.
Ray parallel to axis after refraction passes through F (convex) or appears to come from F (concave).
Ray through optical centre goes undeviated.

Board vs CBSE

CBSE combines reflection and refraction into a single Class 10 chapter. Maharashtra splits them, but the physics is the same. Master ray-diagram conventions and the sign of u, v, f — half of your marks depend on it.