Light – Complete Guide For Class 8 Science Chapter 13

Welcome to iPrep, your Learning Super App! Our learning resources for the chapter, Light Class 8th chapter 13 is designed to ensure that you grasp this concept with clarity and perfection. Whether you’re studying for an upcoming exam or strengthening your concepts, our engaging animated videos, practice questions and notes offer you the best of integrated learning with interesting explanations and examples.

The chapter on Light in Class 8 Science introduces students to the fundamental principles of how light behaves and interacts with various objects. It covers essential concepts such as the difference between luminous and non-luminous objects, the laws of reflection, and the formation of images by plane mirrors. This topic covers the phenomena of dispersion, the human eye, and its functions, and common eye defects and their corrections. It also provides a comprehensive understanding of light, its properties, and its significance in our daily lives.

Two Categories of Objects

Objects can be classified into two main categories: Luminous and Non-luminous.

Luminous Objects

Luminous objects emit their own light, making them easily visible even in the dark. Examples include:

• The Sun
• Light bulbs
• Torch bulbs
• Candle flames

Non-luminous Objects

Non-luminous objects do not emit light on their own. We see them because they reflect light from luminous sources. Examples include:

• Tables
• Chairs
• Humans
• Bicycles

Non-luminous Objects Classification

Non-luminous objects can be further categorized based on their transparency:

• Opaque: Do not allow light to pass through.
• Transparent: Allow light to pass through completely.
• Translucent: Allow light to pass through partially.

The Role of Light in Visibility

To see objects, our eyes are essential. However, in the dark, we cannot see non-luminous objects because there is no light to reflect them. During the day, sunlight helps us see objects. At night, we rely on artificial light sources like bulbs and lamps.

How We See Non-luminous Objects

Luminous objects are visible because they emit light. Non-luminous objects become visible when light falls on them and is reflected to our eyes.

Shiny Surfaces and Mirrors

Shiny surfaces can reflect light. These surfaces can be flat, like plane mirrors, or curved, like spherical mirrors. There are two types of spherical mirrors:

• Convex mirrors
• Concave mirrors

Reflection of Light

Flat Shiny Surfaces: Plane Mirrors

When light hits a plane mirror, it is reflected back. The law of reflection states:

1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, reflected ray, and the normal to the point of incidence all lie in the same plane.

Image Formation by Plane Mirrors

Images formed by plane mirrors have distinct characteristics:

• They are erect.
• They are the same size as the object.
• They are equidistant from the mirror as the object.
• They are laterally inverted (left and right sides are swapped).

Types of Reflection

Regular Reflection Occurs when parallel rays of light hit a smooth surface and remain parallel after reflection.

Diffused Reflection Occurs when parallel rays hit a rough surface and scatter in different directions.

Multiple Images and Kaleidoscopes

Using multiple mirrors can create multiple images of an object. The formula to calculate the number of images formed is:

The Kaleidoscope

A kaleidoscope uses mirrors to create beautiful patterns. To make one, you need:

• Three rectangular glass strips
• A circular piece of cardboard
• A cardboard tube
• A circular plane glass plate
• Ground glass plate
• Pieces of broken bangles
• Transparent plastic sheet
• Adhesive

Steps:

1. Fix the glass strips inside the cardboard tube.
2. Attach a transparent sheet to a circular cardboard piece with a hole in the center.
3. Close one end of the tube with this disc.
4. Attach the circular glass plate to the other end.
5. Place broken bangles inside and cover with the ground glass plate.

Interesting Light Phenomena

When light interacts with different surfaces and mediums, it can create various effects:

• CDs appear colored
• Rainbows form
• Soap bubbles show colors
• Light through a prism splits into colors

Dispersion of Light

Light consists of seven colors (VIBGYOR). When it splits into these colors, the phenomenon is called dispersion. A common example is the formation of a rainbow.

The Human Eye

The eye has several parts:

• Ciliary muscle
• Iris
• Pupil
• Lens
• Optic nerve
• Cornea
• Retina

Each part plays a crucial role in focusing light and creating vision. The iris controls the amount of light entering the eye, and the retina is where the light is focused to form images.

Eye Defects and Their Corrections

Common eye defects include:

• Near-sightedness: Corrected with convex lenses.
• Far-sightedness: Corrected with concave lenses.
• Cataract: Treated with surgery.

Eye Care Tips

• Avoid reading in poor light.
• Do not look directly at bright lights.
• Wash your eyes with clean water if dust enters.
• Consult a doctor if you have persistent eye problems.

Importance of Vitamin A

Vitamin A is crucial for eye health. Foods rich in Vitamin A include:

• Milk products (butter, curd, cheese)
• Green vegetables (spinach, broccoli)
• Red vegetables (carrots)
• Fruits (mango, papaya)
• Cod liver oil
• Eggs

Aids for Visual Impairment

Optical Aids

• Bifocal lenses
• Contact lenses
• Tinted lenses
• Magnifiers

Non-optical Aids

• Visual aids (magnified words, suitable lighting)
• Tactual aids (Braille typewriters, slates, styluses)

• Auditory aids (cassettes, tape recorders, talking books)

• Electronic aids (talking calculators, CCTV, audio CDs, voice boxes)

The Braille System

Developed by Louis Braille, this system uses a 63-dot pattern for characters, allowing visually impaired individuals to read and write.

This chapter provides a comprehensive understanding of the concepts of light, reflection, and vision. It delves into the nature of light, distinguishing between luminous and non-luminous objects and explaining how we see objects through the reflection of light. The laws of reflection are thoroughly covered, including practical examples such as the behavior of plane mirrors and the phenomenon of lateral inversion. This topic also explores the dispersion of light, explaining how white light splits into its constituent colors, creating phenomena like rainbows. The anatomy and function of the human eye are discussed in detail, helping students understand how we perceive images and colors. Common eye defects such as near-sightedness, far-sightedness, and cataracts are explained, along with their respective corrections using lenses and surgical procedures. By understanding these concepts, students gain valuable insights into the mechanisms of vision and the behavior of light, enhancing their comprehension of everyday phenomena.