Light Class 10 Notes – Light Reflection and Refraction Science Chapter 10

Light Class 10 Notes

Light is a type of energy that allows humans to see.

Light comes from a source and bounces off objects that our eyes sense, and our brain analyses this signal, allowing us to see.

Maxwell predicted that magnetic and electric fields travel in waves that travel at the speed of light. This prompted Maxwell to anticipate that light was transported by electromagnetic waves, implying that light has the electromagnetic property.

Introduction to the light class 10 notes

some important definitions

Light Reflection: The phenomenon of light bouncing back into the same medium by a smooth surface is known as reflection. The light that falls on the surface is referred to as incident light.

Reflected light: Light that returns after reflection is referred to as reflected light. The angle of incidence is defined as the angle formed by the incident ray and the normal. A reflection angle is an angle formed by the reflected beam and the normal.

Mirror: A mirror is a surface that can reflect light.

Plane Mirror: A plane mirror has a plane reflecting surface.

Spherical Mirror: A spherical mirror is one in which the reflecting surface is part of a hollow sphere.
There are two kinds of spherical mirrors.

Convex mirror: The reflecting surface of this mirror is convex. Because it diverges the light, it is also known as a diverging mirror.

Concave mirror: The reflecting surface of this mirror is concave. Because it converges the light, it is also known as a converging ‘mirror.

how is an Image Formed using Special Rays?

After reflection, a ray of light parallel to the major axis of a spherical mirror converges or diverges from focus. A ray of light travelling through or appearing from the spherical mirror’s center of curvature is reflected along the same path. A light ray travelling through or appearing from the focus of a spherical mirror becomes parallel to the main axis. A light ray incident at the pole of a spherical mirror is reflected at the same angle as the primary axis.

Light characteristics

The speed of light is denoted by c=λμ, where λ is its wavelength and μ is its frequency. The constant speed of light is 2.998108m/s, or about 3.0108m/s.
Linear Magnification is the ratio of the image’s height to the object’s height.
m=h’h…where m = magnification, h = picture height, and h’ = object height


Refraction of Light is defined as the bending of light at the junction of two distinct media.

If the velocity of light in a medium is greater, the medium is said to be optically rarer. For example, air or vacuum is optically rarer.

If the velocity of light in a medium is lower, the medium is said to be optically denser. Glass, for example, is denser than air.

The quantity or extent of bending of light when it flows from one medium to another is represented by the refractive index. The refractive index is classified into two sorts. Absolute refractive index and relative refractive index.

Refraction Laws

The refraction law is called Snell’s law of refraction and it states that “At the point of incidence, the incident ray refracted ray, and normal to the interface of two transparent media all lie in the same plane”. For a given color of light and a given set of media, the sine of the angle of incidence to the sine of the angle of refraction is constant.

Refraction of light through Rectangular glass slab

When light strikes a rectangular glass slab, it emerges parallel to the incident beam and is displaced laterally. It progresses from rarer to a denser medium, then back to a rarer medium.

Refraction of light through Rectangular glass slab
Refraction through rectangular glass slab-light class 10 notes

Planar surface refraction

Light bends towards the normal while passing from a rarer to a denser medium at the surface of the two media, according to Snell’s Law. When light moves from a denser to a rarer medium at the surface of contact, it bends away from the normal.

Total Internal reflection

when light passes through a denser medium and into a rarer medium, it bends away from the normal. The critical angle is the angle at which the incident ray causes the refracted ray to go parallel to the surface of the two media. When the incidence angle is greater than the critical angle, it reflects rather than refracts inside the denser material. Total Internal Reflection is the name given to this experience. E.g. mirages and optical filers.

Propagation of light

light class 10 notes use the Fermat theorem to make students learn how light propagates through different mediums.

The Fermat Principle: Light always takes the shortest path between any two points, according to the concept of least time (which may not be the shortest path). Fermat’s principle of least time can be used to validate rectilinear light propagation and the law of reflection [i=r].

Fermat’s Principle in Action: 1. As a result of Fermat’s Principle, we can make some observations that will be beneficial as we explore the area of geometric optics: Light beams are rectilinear in a homogenous medium. Light travels in a straight line in any medium with a constant index of refraction.
2. A surface’s angle of reflection equals its angle of incidence. This is known as the Law of Reflection.

Fermat’s example in reality: Mirage is a good example of this. Sometimes we think we see water on the road, but when we get there, it’s dry. What we see is the light from the sky reflected on the road. Because the air is very hot right above the road, but cooler farther up. Because hot air expands more than cool air and is thinner, the speed of light decreases less.

Image formation by Mirrors

  • Images can be real or virtual, upright or upside down, amplified or reduced.
  • The actual convergence of light beams creates a real image.
  • The apparent convergence of divergent light rays is a virtual image.
  • If an image is generated upside down, it is called inverted; otherwise, it is called erect.
  • The picture generated is said to be magnified if it is larger than the object.
  • If the created image is smaller than the object, it is diminished.
  • When a spherical mirror’s image is actual, it is also inverted and on the same side of the mirror as the object. The magnification is negative since both v and u are negative.

Also Check – Chemical Reactions and Equations Class 10 Notes – CBSE Science Chapter 1

A virtual image generated by a spherical mirror is also erect and is on the opposite side of the mirror as the item. Because u is –ve and v is +ve in this situation, m is positive.

The mirror formula is expressed as 1/u+1/v = 1/f.

Light class 10 notes

The statement Light Reflection and Refraction Class 10 Notes Science Chapter 10 img-2 describes linear magnification.

  • The frequency of light does not vary as it travels from one medium to another.
  • Light refracts due to the varying velocity of light in different mediums.
  • The refraction of light is governed by two laws:
  • At the point of incidence, the incident ray, the refracted ray, and the normal are all in the same plane.
  • The sine of the angle of incidence divided by the sine of the angle of refraction is a constant.
Image formation by Mirrors
Image formation by Concave mirror- light class 10 notes


Image Formation by Lens

Spherical lenses are created by connecting two spherical transparent surfaces. Spherical lenses made by joining two spherical surfaces that bulge outward are known as convex lenses, whereas concave lenses are formed by joining two spherical surfaces that bend inward. When light strikes a curved surface and passes through it, the rules of refraction still apply. Consider lenses.

Image Formation by Lens

Important spherical lens terminology mentioned in light class 10 notes

  • The Optical Centre (P) of a spherical lens is the halfway or symmetric center. It is sometimes referred to as the pole.
  • The line that runs through the optical center and the center of curvature is known as the principal axis.
  • A paraxial ray is both close to and parallel to the primary axis.
  • The centers of the spheres that the spherical lens was a part of were referred to as the center of curvature (C). A spherical lens has two curvature centers.
  • Focus (F): The point on a lens’s axis at which parallel rays of light appear to converge or diverge after refraction.
  • Focal length is the distance between the focus and the optical center in any lens.
  • Diverging lens: Concave lens
  • Converging lens: Convex lens Ray diagram rules for representing formed pictures. A light ray parallel to the major axis travels through/appears to pass through the focus. A ray that passes through the optical center has no deviation.
Important spherical lens terminology
Image formation by convex lens-light class 10 notes

Magnification and lens formula

The relationship between the object-distance (u), image-distance (v), and focal length (f) of a spherical lens is given by the lens formula: 1/v = 1/u = 1/f.

Spherical lens applications

Visual aids such as spectacles, binoculars, magnifying lenses, and telescopes are examples of applications.

The Power of Lens

The power of a lens is equal to the reciprocal of its focal length, i.e. 1/f (in metre). The SI unit of lens power is dioptre (D).

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