Foundation Batch For Class 7

LIGHT

EXPLORING THE NATURE OF LIGHT

Introduction

Light is a form of energy that enables us to see objects. This chapter explores the behavior of light, its properties, and how it interacts with various objects, creating shadows, reflections, and images.

1. Properties of Light

Travels in a Straight Line: Light moves in straight paths, demonstrated by shining a torch through a narrow slit.
Speed of Light: Light travels at 3×10^8 m/s in a vacuum.
Reflection: Light bounces off smooth surfaces.
Refraction: Light bends when passing through different mediums (e.g., air to water).

2. Reflection of Light

Key Terms

Incident Ray: Light ray striking a surface.
Reflected Ray: Light ray bouncing off the surface.
Normal: An imaginary line perpendicular to the surface at the point of incidence.
Angle of Incidence (i): Angle between the incident ray and the normal.
Angle of Reflection (r): Angle between the reflected ray and the normal.

Laws of Reflection

Angle of incidence equals the angle of reflection (i=r).
Incident ray, reflected ray, and the normal lie in the same plane.

3. Types of Reflection

Regular Reflection: Occurs on smooth surfaces (e.g., mirrors). Produces clear images.
Irregular Reflection: Occurs on rough surfaces (e.g., walls). Scatters light, producing no clear image.

4. Formation of Images in Mirrors

Plane Mirrors

Forms virtual, upright, and same-size images.
Lateral inversion occurs (left appears as right and vice versa).

Curved Mirrors

Concave Mirror: Produces magnified or diminished images depending on the object’s distance.
- Used in telescopes and shaving mirrors.
Convex Mirror: Produces smaller, virtual, and upright images.
- Used as rear-view mirrors in vehicles.

5. Refraction of Light

When light passes from one medium to another (e.g., air to water), its speed changes, causing it to bend.
Example: A pencil appears bent when placed in a glass of water.

Applications of Refraction

Lenses in spectacles.
Magnifying glasses.
Prism experiments (splitting white light into a spectrum).

6. Dispersion of Light

Splitting of white light into seven colors (VIBGYOR) by a prism.
Colors of the Spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, and Red.
Example: Rainbow formation after rain.

7. The Human Eye

Structure

Cornea: Transparent front part that refracts light.
Iris and Pupil: Control the amount of light entering the eye.
Lens: Focuses light on the retina.
Retina: Contains light-sensitive cells that send signals to the brain.
Optic Nerve: Transmits signals from the retina to the brain.

Care for Eyes

Avoid reading in dim light or very bright light.
Take breaks during prolonged screen time.
Eat foods rich in Vitamin A.

8. Shadows

How Shadows Form

Shadows are created when an opaque object blocks light.
Characteristics:
1. Shadow size depends on the distance of the light source.
2. Sharp shadows are formed when the source is small or close.

Activity:

Shine a torch on an object to observe shadow formation.

9. Fun Facts and Activities

Shadow Play: Create animal shapes using your hands and a torch.
Periscope: Build a simple periscope using two mirrors to see over obstacles.

10. Practice Questions

Define the laws of reflection.
Differentiate between regular and irregular reflection.
Explain the phenomenon of refraction with an example.
What are the uses of concave and convex mirrors?
Describe how a rainbow is formed.

11. Summary

Light travels in straight lines and reflects or refracts upon interacting with surfaces.
Mirrors and lenses are tools that manipulate light to form images.
Understanding light helps in designing optical devices and understanding natural phenomena like rainbows.

📘 MCQs: LIGHT (Exploring the Nature of Light)

🟢 Easy Level (1–20)

Light is a form of:
A) Matter
B) Energy
C) Force
D) Sound
Light travels in:
A) Curved line
B) Zig-zag
C) Straight line
D) Circular path
The speed of light in vacuum is:
A) 3×10⁶ m/s
B) 3×10⁸ m/s
C) 3×10⁵ m/s
D) 3×10⁷ m/s
Reflection means:
A) Bending of light
B) Splitting of light
C) Bouncing of light
D) Absorption of light
A mirror shows:
A) Shadow
B) Image
C) Reflection only
D) Refraction
The angle between incident ray and normal is:
A) Reflection
B) Incidence
C) Refraction
D) Deviation
Plane mirrors form images that are:
A) Real
B) Virtual
C) Inverted
D) Smaller
Lateral inversion means:
A) Upside down
B) Left-right change
C) Bigger image
D) Smaller image
Convex mirrors form images that are:
A) Real
B) Inverted
C) Smaller
D) Larger
Concave mirrors are used in:
A) Rear-view mirrors
B) Shaving mirrors
C) Windows
D) Doors
Refraction occurs when light:
A) Reflects
B) Stops
C) Changes medium
D) Absorbs
A pencil appears bent in water due to:
A) Reflection
B) Refraction
C) Dispersion
D) Absorption
White light splits into colors by:
A) Mirror
B) Lens
C) Prism
D) Water
Rainbow has how many colors?
A) 5
B) 6
C) 7
D) 8
VIBGYOR stands for:
A) Colors
B) Energy
C) Light speed
D) Waves
Shadow is formed by:
A) Transparent objects
B) Opaque objects
C) Water
D) Air
The human eye helps in:
A) Hearing
B) Seeing
C) Smelling
D) Touching
Retina contains:
A) Muscles
B) Nerves
C) Light-sensitive cells
D) Bones
Light cannot pass through:
A) Glass
B) Water
C) Air
D) Wood
Regular reflection occurs on:
A) Rough surface
B) Smooth surface
C) Cloth
D) Paper

🟡 Moderate Level (21–40)

Laws of reflection state:
A) i ≠ r
B) i = r
C) i > r
D) i < r
Incident ray, reflected ray, and normal lie in:
A) Same line
B) Same plane
C) Different planes
D) Different directions
Convex mirrors are used in vehicles because:
A) They enlarge objects
B) They show wider area
C) They absorb light
D) They bend light
Concave mirrors can form:
A) Only real images
B) Only virtual images
C) Both real and virtual
D) No image
Irregular reflection occurs on:
A) Smooth surfaces
B) Polished surfaces
C) Rough surfaces
D) Mirrors
Refraction depends on:
A) Speed of light
B) Medium
C) Angle
D) All of these
The bending of light is due to:
A) Speed change
B) Temperature
C) Pressure
D) Gravity
Dispersion occurs due to:
A) Reflection
B) Refraction
C) Different speeds of colors
D) Absorption
Red light bends:
A) Most
B) Least
C) Same
D) None
Violet light bends:
A) Least
B) Most
C) Same
D) None
A shadow is longest when:
A) Sun overhead
B) Sun low
C) Night
D) Noon
The pupil controls:
A) Image
B) Light entry
C) Reflection
D) Refraction
The cornea helps in:
A) Hearing
B) Smelling
C) Refraction
D) Reflection
Optical devices use:
A) Sound
B) Light
C) Heat
D) Pressure
A periscope uses:
A) Refraction
B) Reflection
C) Dispersion
D) Absorption
Transparent objects:
A) Block light
B) Allow light
C) Reflect light
D) Absorb light
Opaque objects:
A) Allow light
B) Block light
C) Bend light
D) Split light
Magnifying glass uses:
A) Mirror
B) Lens
C) Prism
D) Shadow
A lens works on:
A) Reflection
B) Refraction
C) Dispersion
D) Absorption
Image in plane mirror is:
A) Real
B) Virtual
C) Inverted
D) Enlarged

🔴 Difficult Level (41–50)

If angle of incidence is 30°, angle of reflection is:
A) 60°
B) 30°
C) 15°
D) 45°
A convex mirror always forms:
A) Real image
B) Virtual image
C) Inverted image
D) Enlarged image
Which device uses dispersion?
A) Mirror
B) Prism
C) Lens
D) Eye
Speed of light is maximum in:
A) Water
B) Glass
C) Air
D) Vacuum
Refraction causes:
A) Image inversion
B) Bending of light
C) Shadow formation
D) Reflection
Which color has highest wavelength?
A) Violet
B) Blue
C) Red
D) Green
Which color has lowest wavelength?
A) Red
B) Yellow
C) Violet
D) Orange
Real images are:
A) Upright
B) Inverted
C) Same size
D) Always virtual
The image distance in plane mirror is:
A) Less than object distance
B) More than object distance
C) Equal to object distance
D) Zero
A shadow becomes sharper when:
A) Light source is big
B) Light source is small
C) Object is far
D) Light is weak

✅ Answers

1-B, 2-C, 3-B, 4-C, 5-B
6-B, 7-B, 8-B, 9-C, 10-B
11-C, 12-B, 13-C, 14-C, 15-A
16-B, 17-B, 18-C, 19-D, 20-B

21-B, 22-B, 23-B, 24-C, 25-C
26-D, 27-A, 28-C, 29-B, 30-B
31-B, 32-B, 33-C, 34-B, 35-B
36-B, 37-B, 38-B, 39-B, 40-B

41-B, 42-B, 43-B, 44-D, 45-B
46-C, 47-C, 48-B, 49-C, 50-B