10th Physics Federal Board Notes Chapter 14 Optics

10th Physics Federal Board Notes: Chapter 14 Optics

Complete solved exercises with MCQs, short questions, and long questions. Perfect preparation for 10th class physics exams.

10th Physics Federal Board Chapter 14 Notes Optics Reflection Refraction Lenses Mirrors Reading Time: 20 min

📋 Table of Contents

1. Multiple Choice Questions (MCQs)
2. Constructed Response Questions
- 2.1 Seven Color Pattern Experiment
3. Short Answer Questions
4. Long Answer Questions

🔬 Introduction to Optics

Chapter 14: Optics explores the fundamental principles of light behavior including reflection, refraction, dispersion, and image formation. This chapter covers essential concepts like laws of reflection and refraction, total internal reflection, working of lenses and mirrors, human vision, and practical applications in daily life and technology. Understanding optics is crucial for comprehending how we see the world and developing optical instruments.

Multiple Choice Questions (MCQs)

1. A glass slab is dipped in a transparent liquid having same refractive index as that of glass slab. We cannot see the boundary of the two media (glass and liquid) due to ______ refraction.

A. Maximum

B. Minimum

C. Zero

D. Unit

Correct Answer: C
When two media have the same refractive index, light passes without bending, making the boundary invisible.

20. The rods and cones a human eye has are:

A. 6 million and 100 million

B. 100 million and 6 million

C. 6 million and 6 million

D. 100 million and 100 million

Correct Answer: B
Human eyes contain about 100 million rods (night vision) and 6 million cones (color vision).

Constructed Response Questions

Q1. Take some water in the bowl and put a small mirror in it such that some part of mirror is dipped in the water. Fall sunlight on the mirror in such a way that the reflection of mirror appears on the wall or white board of the class.

(a) Why the seven color pattern is shown on the wall?

The seven-color pattern appears due to dispersion of white light. When sunlight passes through water, it refracts and separates into its constituent colors (VIBGYOR) because different colors bend at different angles. The mirror reflects this dispersed light onto the wall, creating the rainbow pattern.

(b) What is the role of water in this phenomenon?

Water acts as a prism that causes refraction and dispersion. Its different refractive index compared to air bends light rays and separates white light into its spectrum of colors, enabling us to see the individual colors that make up sunlight.

The fundamental principle is dispersion through refraction. When white light enters water from air, it slows down and bends. Since different colors have different wavelengths, they refract at slightly different angles. Violet light bends the most while red bends the least, causing the separation into seven colors that we perceive as a spectrum.

Short Answer Questions

15. Propose a reason for producing more sound by an empty container as compared to a filled one.

📦 Sound Production in Containers

Empty containers produce louder sound due to:

Air Resonance: Empty space allows air column vibration
Less Damping: No material to absorb vibration energy
Greater Amplitude: Unrestricted vibration creates larger sound waves
Resonance Frequency: Empty containers vibrate at their natural frequency

Filled containers damp vibrations, reducing sound intensity.

Long Answer Questions

1. What is reflection of light? Also explain the laws of reflection.

🔦 Reflection of Light

Reflection is the phenomenon where light rays bounce back when they hit a surface. The bouncing follows specific rules called the Laws of Reflection.

📜 Laws of Reflection

First Law: The angle of incidence equals the angle of reflection

\[ \theta_i = \theta_r \]

Second Law: The incident ray, reflected ray, and normal all lie in the same plane

Key Terms:

Incident Ray: Light ray approaching the surface
Reflected Ray: Light ray bouncing back from surface
Normal: Imaginary line perpendicular to surface at point of incidence
Angle of Incidence (θᵢ): Angle between incident ray and normal
Angle of Reflection (θᵣ): Angle between reflected ray and normal

2. Discuss the types of reflection.

Specular Reflection	Diffuse Reflection
Surface: Smooth, polished like mirrors	Surface: Rough, uneven like paper, walls
Ray Behavior: Parallel rays remain parallel after reflection	Ray Behavior: Parallel rays scatter in different directions
Image Formation: Forms clear, sharp images	Image Formation: No image formation, only illumination
Examples: Mirrors, still water, metal surfaces	Examples: Paper, wood, cloth, most objects

3. How images are formed in plane mirrors? Explain.

🪞 Plane Mirror Image Formation

Process:

Light rays from object strike mirror surface
Rays reflect according to laws of reflection
Reflected rays diverge (spread out)
Our eyes trace these rays backward in straight lines
Virtual image forms where these backward extensions meet

Image Characteristics:

Virtual: Cannot be projected on screen
Erect: Same orientation as object
Same Size: No magnification or reduction
Laterally Inverted: Left-right reversed
Same Distance: Image as far behind mirror as object in front

4. Describe the position and characteristics of images formed by plane mirrors.

📍 Position

Image appears behind mirror at same distance as object is in front

🔄 Orientation

Erect (upright) but laterally inverted (left-right reversed)

📏 Size

Same size as object - no magnification or minification

🎯 Nature

Virtual - cannot be captured on screen, only seen by eyes

5. Elaborate the refraction of light and the laws of refractions.

💡 Refraction of Light

Refraction is the bending of light when it passes from one transparent medium to another due to change in speed.

📜 Laws of Refraction (Snell's Law)

First Law: Incident ray, refracted ray, and normal all lie in same plane

Second Law (Snell's Law): Ratio of sine of angles is constant

\[ n_1 \sin\theta_1 = n_2 \sin\theta_2 \]

Where:

n₁ = refractive index of first medium
θ₁ = angle of incidence
n₂ = refractive index of second medium
θ₂ = angle of refraction

Bending Rules:

Light bends toward normal when entering denser medium
Light bends away from normal when entering rarer medium

6. Analyze the speed of light in material medium.

⚡ Light Speed in Materials

Fundamental Principle: Light slows down in material media compared to vacuum

\[ v = \frac{c}{n} \]

Where v = speed in medium, c = speed in vacuum (3×10⁸ m/s), n = refractive index

Examples:

Vacuum: v = 3.00 × 10⁸ m/s (n = 1.0)
Air: v ≈ 2.99 × 10⁸ m/s (n ≈ 1.0003)
Water: v ≈ 2.26 × 10⁸ m/s (n ≈ 1.33)
Glass: v ≈ 2.00 × 10⁸ m/s (n ≈ 1.5)
Diamond: v ≈ 1.24 × 10⁸ m/s (n ≈ 2.42)

Reason: Light interacts with electron clouds in atoms, causing absorption and re-emission delays.

7. What is refractive index? Elaborate your answer.

📊 Refractive Index Concept

Definition: Refractive index measures how much a medium slows down light compared to vacuum.

\[ n = \frac{c}{v} \]

Where n = refractive index, c = speed in vacuum, v = speed in medium

Alternative Formulas:

\[ n = \frac{\sin i}{\sin r} \quad \text{(Snell's Law)} \]

\[ n = \frac{1}{\sin C} \quad \text{(Critical angle)} \]

\[ n = \frac{\text{Real depth}}{\text{Apparent depth}} \]

Common Values:

Vacuum: 1.0000 (by definition)
Air: 1.0003
Water: 1.33
Glass: 1.5 - 1.9
Diamond: 2.42

8. Differentiate total internal reflection from reflection. Also derive a relation for critical angle.

Regular Reflection	Total Internal Reflection (TIR)
Occurs at any interface	Only when light travels from denser to rarer medium
Works at any angle of incidence	Requires angle greater than critical angle
Partial reflection with some transmission	Complete reflection with no transmission
Reflected intensity less than incident	Almost 100% reflection efficiency

🧮 Critical Angle Derivation

Critical Angle (θc) is the angle of incidence when refracted angle is 90°

From Snell's Law: \( n_1 \sin\theta_1 = n_2 \sin\theta_2 \)

At critical angle: \( \theta_1 = \theta_c \), \( \theta_2 = 90^\circ \)

So: \( n_1 \sin\theta_c = n_2 \sin 90^\circ \)

Since \( \sin 90^\circ = 1 \): \( n_1 \sin\theta_c = n_2 \)

Therefore: \( \sin\theta_c = \frac{n_2}{n_1} \)

Final formula: \( \theta_c = \sin^{-1}\left(\frac{n_2}{n_1}\right) \)

Condition: n₁ > n₂ (light going from denser to rarer medium)

9. Enlist the uses of fiber optics in telecommunication system.

🌐 Internet Backbone

High-speed data transmission for broadband internet services

📞 Telephone Networks

Crystal clear voice communication over long distances

📺 Cable TV

High-quality video and audio signal transmission

🛰️ Undersea Cables

Global internet connectivity between continents

🏥 Medical Imaging

Endoscopes and internal examination tools

🔧 Industrial Control

Factory automation and control systems

🎯 Military Applications

Secure communication and guidance systems

🏙️ Smart Cities

Traffic management and public safety networks

10. Illustrate thin lenses. Also explain behavior of converging and diverging lens to parallel beam of light.

🔍 Thin Lenses

Definition: Lenses whose thickness is negligible compared to their focal length and radii of curvature.

Types:

Converging (Convex) Lenses: Thicker in middle, converge light rays
Diverging (Concave) Lenses: Thinner in middle, diverge light rays

Converging Lens	Diverging Lens
Shape: Thick center, thin edges	Shape: Thin center, thick edges
Parallel Rays: Converge to focal point	Parallel Rays: Diverge from focal point
Focal Length: Positive	Focal Length: Negative
Image Types: Real and virtual	Image Types: Always virtual

11. Evaluate how images are formed by converging lens using ray diagram.

📐 Converging Lens Image Formation

Ray Diagram Rules:

Ray parallel to principal axis passes through focal point after refraction
Ray through optical center continues straight without deviation
Ray through focal point becomes parallel to principal axis after refraction

Image Cases:

Object beyond 2F: Real, inverted, diminished image between F and 2F
Object at 2F: Real, inverted, same size image at 2F
Object between F and 2F: Real, inverted, enlarged image beyond 2F
Object at F: No image (rays parallel)
Object between F and lens: Virtual, erect, enlarged image on same side

12. Differentiate between real and virtual images.

Real Image	Virtual Image
Formed by actual intersection of light rays	Formed by apparent intersection of light rays
Can be projected on screen	Cannot be projected on screen
Always inverted	Always erect
Formed by converging lenses/mirrors	Formed by diverging lenses/mirrors
Examples: Camera image, projector screen	Examples: Mirror image, magnifying glass

13. Assess linear magnification as a property of thin lenses.

📏 Linear Magnification

Definition: Ratio of image height to object height, or image distance to object distance

\[ m = \frac{h_i}{h_o} = -\frac{v}{u} \]

Interpretation:

m > 0: Upright image (virtual)
m < 0: Inverted image (real)
|m| > 1: Magnified image
|m| < 1: Diminished image
|m| = 1: Same size image

Applications: Used in designing optical instruments like microscopes, telescopes, cameras

14. Discuss the dispersion of light through a prism.

🌈 Dispersion by Prism

Definition: Separation of white light into its constituent colors (spectrum)

Process:

White light enters prism and refracts
Different colors have different wavelengths
Different wavelengths refract at different angles
Violet bends most (short wavelength)
Red bends least (long wavelength)
Colors separate into VIBGYOR spectrum

Color Order: Violet, Indigo, Blue, Green, Yellow, Orange, Red

Applications: Spectroscopy, rainbow formation, optical instruments

15. Design some single lens optical devices.

🔍 Magnifying Glass

Convex lens for reading small print and detailed inspection

👓 Eyeglasses

Convex for farsightedness, concave for nearsightedness correction

📷 Camera Lens

Convex lens for focusing light onto film or sensor

🔦 Spotlight

Convex lens to concentrate light into focused beam

👁️ Peephole

Concave lens for wide-angle door viewing

💡 Projector

Convex lens for enlarging and focusing images on screen

16. Analyze the visible spectrum of electromagnetic radiations.

👁️ Visible Spectrum Analysis

Range: 400 nm to 750 nm wavelength

Color Distribution:

Violet: 400-450 nm (highest energy)
Blue: 450-495 nm
Green: 495-570 nm
Yellow: 570-590 nm
Orange: 590-620 nm
Red: 620-750 nm (lowest energy)

Human Vision: Our eyes contain rods (brightness) and cones (color) that detect this range

Importance: Enables color vision, essential for art, design, warning signals, and natural beauty appreciation

17. Illustrate human eye and color perception.

👁️ Human Eye Structure

Key Components:

Cornea: Transparent front covering
Iris: Colored part controlling pupil size
Lens: Focuses light onto retina
Retina: Light-sensitive layer with photoreceptors
Rods: 100 million, for low-light vision
Cones: 6 million, for color vision (S,M,L types)

Color Perception:

S-cones: Detect blue light (short wavelength)
M-cones: Detect green light (medium wavelength)
L-cones: Detect red light (long wavelength)
Brain Processing: Combines signals for full color vision

18. Outline short-sightedness and long-sightedness also explain how they can be fixed?

Short-Sightedness (Myopia)	Long-Sightedness (Hyperopia)
Problem: Distant objects blurry	Problem: Near objects blurry
Cause: Eyeball too long	Cause: Eyeball too short
Image Forms: In front of retina	Image Forms: Behind retina
Correction: Concave (diverging) lens	Correction: Convex (converging) lens
Effect: Spreads light before eye	Effect: Converges light before eye

19. Define and explain gravitational lensing.

🌌 Gravitational Lensing

Definition: Bending of light by gravitational fields of massive objects

Mechanism:

Massive objects warp spacetime according to General Relativity
Light follows curved paths in warped spacetime
Acts like optical lens but uses gravity instead of refraction

Effects:

Einstein Rings: Perfect circular images
Multiple Images: Same object appearing multiple times
Magnification: Brightening of distant objects

Applications: Studying dark matter, distant galaxies, testing General Relativity

20. Explain acoustic lensing and its applications.

🔊 Acoustic Lensing

Definition: Acoustic lensing is the phenomenon where sound waves are focused or redirected using specially designed structures or materials, analogous to how optical lenses manipulate light waves. It involves creating variations in acoustic impedance to bend and focus sound waves.

Key Principles:

Acoustic Impedance: Measure of how much a medium resists sound passage
Refraction of Sound: Sound bends when passing between media with different acoustic properties
Acoustic Lenses: Designed structures that manipulate sound waves in controlled ways

\[ Z = \frac{p}{v} \]

Where Z = acoustic impedance, p = sound pressure, v = particle velocity

🏥 Medical Imaging

Ultrasound focusing for high-resolution medical imaging and therapeutic treatments

🔧 Non-Destructive Testing

Detecting defects and anomalies in materials without causing damage

🌊 Underwater Acoustics

Improving sonar systems for navigation, communication, and detection

🏛️ Architectural Acoustics

Sound focusing in auditoriums and concert halls for better listening experience

🔬 Acoustic Microscopy

High-resolution imaging of small structures and materials using focused sound

🎯 Particle Manipulation

Acoustic tweezers using focused sound waves to move small particles or cells

🎵 How Acoustic Lenses Work

Acoustic lenses can be made from various materials and structures:

Solid Lenses: Materials with different acoustic properties shaped to focus sound
Phononic Crystals: Periodic structures with varying acoustic impedance
Metamaterials: Artificially engineered materials with unique acoustic properties

These structures create controlled variations in acoustic impedance that bend sound waves similar to how optical lenses bend light, enabling precise control over sound propagation and focusing.

📚 Master 10th Physics Optics

This comprehensive guide covers all essential concepts from Chapter 14 Optics. Understanding light behavior, reflection, refraction, and optical instruments is crucial for both academic success and appreciating how we see the world.

Key Topics Covered: Reflection laws, refraction principles, lens working, image formation, human eye, vision defects, and modern optical applications including gravitational and acoustic lensing.

Complete solved exercises based on Federal Board curriculum with detailed explanations and practical applications

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10th Physics Federal Board Notes Chapter 14 Optics - Complete Solved Exercises