⚡ CLASS 10 CBSE PHYSICS — LIGHT (CHANNEL READY MASTER NOTES)
Reflection • Refraction • Mirrors • Lenses • Full Theory + Tricks + PYQs
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🌟 1. LIGHT — BASIC CONCEPT
Light is a form of energy that enables vision. It travels in straight lines in a uniform medium.
📌 KEY PROPERTIES
✔ Rectilinear propagation (straight path)
✔ Reflection
✔ Refraction
✔ Formation of images using mirrors & lenses
🪞 2. REFLECTION OF LIGHT
Reflection = bouncing back of light from a smooth surface.
📌 TYPES
✔ Regular reflection → smooth surface (mirror)
✔ Diffused reflection → rough surface
📌 LAWS OF REFLECTION (VERY IMPORTANT)
1) i = r ✔ Incident ray,
2) reflected ray & normal lie in same plane
🧠 TRICK:
“Same Plane, Same Angle”
🪞 3. SPHERICAL MIRRORS
A mirror which is a part of a hollow sphere.
🌙 CONCAVE MIRROR (CONVERGING MIRROR)
✔ Reflecting surface inward
✔ Converges light rays to focus
✔ Can form real & virtual images
📍 IMAGE FORMATION (MUST LEARN)
✔ Infinity → at F (point image)
✔ Beyond C → between C & F (real, inverted)
✔ At C → at C (same size)
✔ Between C & F → beyond C (enlarged)
✔ Between F & P → virtual, erect, magnified
📌 USES
✔ Torch, headlights
✔ Shaving mirror
✔ Solar concentrator
☀️ CONVEX MIRROR (DIVERGING MIRROR)
✔ Reflecting surface outward
✔ Always forms virtual, erect, diminished image
✔ Wide field of view
📌 USES
✔ Rear view mirrors ✔ Security mirrors
📐 4. IMPORTANT TERMS (DEFINITIONS)
✔ Pole (P): centre of mirror
✔ Focus (F): point where rays meet/appear to meet
✔ Centre of curvature (C): centre of sphere
✔ Radius (R): distance PC
✔ Principal axis: line through P and C
📊 5. MIRROR FORMULA (HIGH SCORING)
🌊 6. REFRACTION OF LIGHT
Refraction = bending of light due to change in speed when medium changes.
📌 WHY IT HAPPENS?
✔ Speed changes in different media ✔ Light bends towards/away from normal
📌 LAWS
✔ i, r and normal lie in same plane
✔ Snell’s law:
\frac{sin i}{sin r} = constant
🧠 TRICK:
Denser → bends towards normal Rarer → bends away
🔍 7. LENSES
Transparent material with at least one curved surface.
🔥 CONVEX LENS (CONVERGING)
✔ Thick in centre
✔ Forms real & virtual images
📍 IMAGE FORMATION
✔ Beyond 2F → between F & 2F (real, inverted)
✔ At 2F → same size
✔ Between F & 2F → beyond 2F (enlarged)
✔ At F → infinity
✔ Between F & O → virtual, erect, magnified
📌 USES
✔ Camera
✔ Microscope
✔ Magnifier
❄️ CONCAVE LENS (DIVERGING)
✔ Thin in centre
✔ Always virtual, erect, diminished image
📌 USES
✔ Door peephole
✔ Optical devices
📊 8. LENS FORMULA
📌 MAGNIFICATION
m =-v/u
⚡ 9. POWER OF LENS
P = 1/f
✔ Unit = Dioptre (D)
✔ Convex → +
✔ Concave → –
📌 10. SIGN CONVENTION (SUPER IMPORTANT)
🌟 COMMON RULE
✔ Object always left side → u negative
✔ Above axis → positive
✔ Below axis → negative
🪞 MIRROR
✔ Concave mirror: f (–), R (–)
✔ Convex mirror: f (+), R (+)
✔ Real image → v (–)
✔ Virtual image → v (+)
🔍 LENS
✔ Convex lens: f (+)
✔ Concave lens: f (–)
✔ Real image → v (+)
✔ Virtual image → v (–)
🎨 11. RAY DIAGRAM TRICK
✔ Ray parallel → passes through F
✔ Ray through F → becomes parallel
✔ Ray through C → reflects back
🧠 TRICK: “FPC RULE”
🔥 12. MOST IMPORTANT QUESTIONS
✔ Mirror formula numericals
✔ Lens formula numericals
✔ Power of lens
✔ Ray diagrams
✔ Refraction reasoning
⚡ 13. QUICK REVISION BOX (ULTIMATE)
✔ i = r
✔ 1/f = 1/v + 1/u
✔ 1/f = 1/v - 1/u
✔ P = 1/f
✔ Convex mirror → always virtual
✔ Concave lens → always virtual
✔ Denser → bends towards normal
🚀 14. EXAM STRATEGY (TOP MARKS)
✔ Write formula first
✔ Apply sign convention
✔ Draw neat diagram
✔ Mention unit
✔ Box final answer
🌟 FINAL LINE
✨ Concepts + diagrams + practice = Full marks guaranteed ✨
🧠⚡ CLASS 10 CBSE — LIGHT CHAPTER MOCK TEST (70 MARKS)
🪞 FULL QUESTION + STEPWISE SOLUTION PAPER
📘 SECTION A — MCQs (1 × 20 = 20)
1.
📌 Q: According to the law of reflection, the angle of incidence is equal to the angle of reflection. What is the correct relation?
A) i > r
B) i < r
C) i = r
D) i + r = 90°
👉 Ans: C) i = r
2.
📌 Q: A convex mirror always forms which type of image?
👉 Ans: Virtual, erect and diminished image
3.
📌 Q: Unit of power of a lens is:
👉 Ans: Dioptre (D)
4.
📌 Q: Light bends when it goes from one medium to another due to:
👉 Ans: Refraction
5.
📌 Q: A concave lens always forms:
👉 Ans: Virtual, erect, diminished image
6.
📌 Q: The mirror formula is:
👉 Ans: 1/f = 1/v + 1/u
7.
📌 Q: A convex lens has focal length:
👉 Ans: Positive
8.
📌 Q: Speed of light is maximum in:
👉 Ans: Vacuum/air
9.
📌 Q: Image formed by plane mirror is:
👉 Ans: Virtual and laterally inverted
10.
📌 Q: A concave mirror focus is:
👉 Ans: Real focus
11–20 (Answers only)
Lens formula → 1/f = 1/v – 1/u
Convex mirror focus → virtual
Refraction occurs due to → change in speed
Magnification (mirror) → m = –v/u
Convex lens is → converging lens
Concave lens is → diverging lens
Object at infinity → image at → focus
Denser medium → light bends → towards normal
Rare medium → light bends → away from normal
Power formula → P = 1/f
📘 SECTION B — VERY SHORT ANSWERS (2 × 7 = 14)
21.
📌 Q: Define reflection of light.
👉 Ans: Reflection is bouncing back of light into the same medium after striking a surface.
22.
📌 Q: State laws of reflection.
✏️ Solution:
✔ Angle of incidence = angle of reflection
✔ Incident ray, reflected ray and normal lie in same plane
👉 Ans: i = r and all rays lie in same plane
23.
📌 Q: Why convex mirror is used in vehicles?
👉 Ans: It gives wide field of view and always forms small upright image.
24.
📌 Q: Define refraction of light.
👉 Ans: Bending of light when it passes from one medium to another due to change in speed.
25.
📌 Q: Write mirror formula.
👉 Ans: 1/f = 1/v + 1/u
26.
📌 Q: Difference between real and virtual image.
👉 Ans:
Real → formed on screen, inverted
Virtual → cannot be formed on screen, erect
27.
📌 Q: Define power of lens.
👉 Ans: Power is reciprocal of focal length in meters.
📘 SECTION C — SHORT NUMERICALS (3 × 7 = 21)
28.
📌 Q: A concave mirror has focal length 10 cm. An object is placed at 20 cm. Find image position.
✏️ Solution:
Given: u = –20 cm, f = –10 cm
👉 Ans: v = –20 cm
29.
📌 Q: A convex lens has focal length 15 cm and object distance 30 cm. Find image distance.
✏️ Solution:
u = –30 cm, f = +15 cm
LCM = 30:
👉 Ans: v = +30 cm
30.
📌 Q: Find power of lens having focal length 50 cm.
✏️ Solution:
f = 0.5 m
P = 1/f = 1/0.5 = 2
👉 Ans: P = +2 D
31.
📌 Q: Why does light bend when it enters glass from air?
👉 Ans: Because speed of light decreases in glass.
32.
📌 Q: Object at infinity in concave mirror—image position?
👉 Ans: At focus (F)
33.
📌 Q: Write magnification formula for mirror.
👉 Ans: m = –v/u
34.
📌 Q: Convex lens image when object is between F and 2F.
👉 Ans: Real, inverted, enlarged image beyond 2F
📘 SECTION D — LONG ANSWERS (5 × 3 = 15)
35.
📌 Q: Explain image formation by concave mirror.
✏️ Solution:
✔ At infinity → image at F
✔ Beyond C → between C and F
✔ At C → same size
✔ Between F and C → enlarged image
✔ Between F and P → virtual image
👉 Ans: Case-wise image formation explained above
36.
📌 Q: Explain refraction of light.
✏️ Solution:
✔ Light changes speed when medium changes
✔ Hence direction changes
✔ Bends towards normal (denser) or away (rarer)
👉 Ans: Refraction due to change in speed of light
37.
📌 Q: Explain image formation by convex lens.
✏️ Solution:
✔ Beyond 2F → between F and 2F
✔ At 2F → same size
✔ Between F and 2F → enlarged
✔ At F → infinity
✔ Between O and F → virtual image
👉 Ans: Case-wise explained above
🎯 FINAL EXAM STRATEGY
✔ Always write “Given”
✔ Write formula first
✔ Apply sign convention carefully
✔ Show steps clearly
✔ Box final answer
200+ MCQ of light chapter
📚 Also Read Class 10 Physics:
Chapter 4: Electric Current & Its Effects
Chapter 11: Human Eye & Colourful World |
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