CBSE Class 8 Science Revision Notes Chapter 16

Class 8 Science Chapter 16 Notes

CBSE Class 8 Science Revision Notes Chapter 16 – Light

According to Class 8 Science Chapter 16, visible light refers to electromagnetic radiation that can be seen by humans. The electromagnetic spectrum is extremely diverse, ranging from low-energy radio waves with wavelengths measured in metres to a high-energy gamma rays with a wavelength less than 1×10-11 metres. Magnetic fields fluctuate and energy is transported at the speed of light by electromagnetic radiation. A stream of photons and massless energy packets are other definitions of light. The photon is the smallest unit of energy that can be moved.

Revision Notes for CBSE Class 8 Science Chapter 16

Access CBSE Class 8 Science Chapter 16 – Light Notes

  1. The natural phenomenon that makes things visible is light. All surfaces reflect light, which is a type of energy.
  2. Luminous objects are things that can produce light on their own. Non-luminous objects are those that lack self-luminous properties. The light shining on them is reflected by them. When an object reflects light, the light enters the eyes, making the object visible.
  3. Consideration of light is the phenomenon of light returning to the same medium after striking a polished or shiny surface.

Types of Reflection:

Regular Reflection: When a parallel beam of light rays strikes either on a smooth or plane surface, the reflected rays will also be parallel. This is referred to as routine reflection. An example of a typical reflection is the reflection produced by a plane mirror.

Diffused or Irregular Reflection: When a light beam strikes a rough or uneven surface, the surface’s irregularities cause the beam to be reflected in a variety of directions.

Multiple reflections are known to exist if the reflected light ray is reflected back after the incident on a different surface. Periscopes operate on the multiple reflections theory. Periscopes are primarily used by soldiers in bunkers, war tanks, and submarines to see distant objects that are not directly visible. The same idea is at play in a kaleidoscope, where multiple reflections lead to the formation of lovely patterns.

Laws of Reflection

The angle of incidence and the angle of reflection are the same.

All three of the incident ray’s components—the ray that strikes the reflecting surface, the incident ray, and the reflected ray—lie in the same plane.

A plane mirror’s ability to reverse images from left to right creates the effect known as lateral inversion. For instance, the left hand will appear to be right when looking in the mirror, and vice versa.

The characteristics of the image formed by a plane mirror:

  • Is the exact same size as the object
  • Inverted left-to-right
  • Virtual and erect
  • Formed behind the mirror at the same height as the thing positioned in front of the mirror.

When two mirrors are angled toward one another, multiple images are created.

White light, also referred to as sunlight, contains seven different hues. Dispersion is the separation of light into its colours. A normal eye can see both nearby and faraway objects.

The Braille writing and reading system allows blind people to read and write. They enhance their interaction with their environment by developing their other senses.

Human Eye and its Parts

  1. The cornea, a transparent spherical membrane, covers the front portion of the eye. The cornea is where light enters the eye.
  2. Aqueous humour, which is present in the space just behind the cornea, is a viscous liquid.
  3. The iris, a muscular diaphragm with a small, circular opening in the middle known as the pupil, is located directly behind the cornea. The absence of light reflection from the pupil is what causes it to be black.
  4. By altering the pupil’s size, the iris is in charge of regulating how much light enters the eye.
  5. The eyes’ convex lenses are made of a clear, proteinaceous material that resembles jelly. The middle of the eye lens is hard, and it gets softer as it gets closer to the edges.
  6. The position of the eye lens is maintained by the ciliary muscles. The ciliary muscles are in charge of adjusting the eye lens’s curvature and focal length.
  7. The retina is the eye’s inner rear surface. It is a semi-transparent, light-sensitive membrane that works like a viewfinder on a camera. The retina contains light-sensitive receptors called rods and cone cells.
  8. Vitreous humour fills the space between the retina and the eye’s lens.

Light Class 8 Science Notes:

The Law of Reflection

Light exhibits very predictable behaviour. A ray of light will behave predictably when reflected according to a law known as the law of reflection if it is observed while it is approaching a flat surface and reflecting. The light ray that approaches the mirror is known as the incident ray, and the light ray that emerges from the mirror is known as the reflected ray.

According to the law of reflection in the Class 8 Science Chapter 16 Notes, a normal line is a line drawn perpendicular to the surface of the point of incidence where this ray strikes. This line creates equal angles from the angle formed by the incident and reflected rays.

The angle formed between the incident ray and the regular ray is known as the angle of incidence. The angle of reflection is the angle formed by the normal and reflected rays.

Regular and Diffused Reflection

Regular and diffused reflection is a significant component of the Class 8 notes for the light chapter. A plane surface, like the surface of a plane mirror, regularly reflects light. After a typical reflection, the reflected rays are parallel, whereas diffused reflection occurs on any rough surface, such as cardboard.

Chapter 16 Science Class 8 Notes: Properties of Mirror Image

The characteristics of an image created by a plane mirror are numerous; they are as follows:

  • They are exactly the same size as the object.
  • They are left-right inverted.
  • They are erect and virtual.
  • They are at the same distance as an object in front of the mirror, it appears behind the mirror.

Class 8 Chapter 16 Science Notes: Braille System

An essential component of the Class 8 Science Light Chapter notes is the braille system. The discovery was made by Louis Braille, and it was developed especially for the blind. It is a touchable raised-dot script that is easily recognisable. Each Braille character is made up of six different dot positions that are arranged in a rectangle with two columns of three dots each. A dot may be raised at any location.

The alphabetic dot patterns, symbols, and other punctuation are all used in braille codes. It is carried out by following a specific consistency and is based on the original assignments made by Louise Braille.  In addition, different Braille codes are used to notate systems such as chess, music, computer programmes, and others. The 64 possible Braille characters and the new notational elements continue to form the foundation of this code.

Notes of Chapter Light Class 8: The Anatomy of the Eye

The human eye is composed of the following components from outside to inside. They are as follows:

  • The eyeball is shielded by the sclera, also known as the white part of the eye.
  • The pupil is the eye’s opening where light enters the body.
  • The iris, which encircles the pupil, regulates how much light should enter the eye by adjusting the pupil’s size.
  • The pupil and iris are protected by the cornea that is present at the window in front of the eye.
  • The retina, which is found at the back of the eye, is illuminated by a clear lens that is positioned behind the pupil and functions as a camera.
  • A crucial component of the eye is the retina. The lining at the back of our eyes is delicate. A cell has ten layers that help it detect light and convert it into an electrical impulse.

FAQs (Frequently Asked Questions)

1. What makes things visible?

An object can be seen only if the light struck by the object enters the eye. Additionally, objects appear in a variety of colours due to their ability to transmit or reflect some colours while absorbing others.

2. State the two laws of reflection.

These are the two laws of reflection:

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

Class 8 notes explain the two laws diagrammatically and in a step-by-step manner.