Light Reflection and Refraction Notes

Let’s learn about light reflection and refraction from class 10 CBSE notes. Different materials reflect light to varying degrees. The two laws of reflection govern light reflection from a smooth surface. A plane mirror’s image is always virtual and erect. A spherical mirror is a spherical mirror with an inwardly curved reflecting surface.

The pole is a point in the centre of a spherical mirror’s reflecting surface. The mirror’s radius of curvature is the radius of the sphere of which the reflecting surface is a part. Focus (or focal point) is the point on the principal axis where all the rays coming from infinity meet or appear to meet.

1st law of reflection:

→ Angle of incidence (i) = Angle of reflection(r)

→ Or angle i  = angle r

2nd law of reflection: 

The incident ray, the reflected ray, and the normal at the point of incidence all lie within the same plane.

The image of a plane mirror is always virtual and erect, and the resulting image is as far back as the object in front of it. These reflection laws hold true for all types of reflecting surfaces, including spherical ones.

Spherical Mirrors

The most common type of curved mirror is the spherical mirror. Such mirrors’ reflecting surfaces can be considered a part of the sphere’s surface. Spherical mirrors have spherical reflecting surfaces.

A concave mirror is one that faces towards the center of the sphere and a convex mirror faces outwards. 

A spoon surface curved inwards or outwards can be approximated to a concave-convex mirror, and a spoon surface that is bulged outwards could be considered convex.

This sphere has a central point. This is known as the center of curvature of a spherical mirror. It is represented by the letter C.

Remember that the mirror does not include the center of curvature. It is located on the opposite side of the reflecting surface. The center of curvature of a concave mirror is in front of it. However, in the case of a convex mirror, it is located behind the mirror.

The radius of curvature of the mirror is the radius of the sphere that contains the reflecting surface of a spherical mirror. It is represented by the letter R. It should be noted that the PC distance equals the radius of curvature. Consider a straight line passing through the pole and the center of curvature of the spherical mirror. This is referred to as the principal axis. Remember that the principal axis of the mirror is normal to it at its pole.

The normal at any point on the spherical mirror is the straight line formed by joining that point to the mirror’s center of curvature.

Focus (or focal point) is the point on the principle axis where all the rays coming from infinity (parallel rays) after reflection either meet or appear to meet is called the focus or the focal point of the mirror. 

The focal length of a spherical mirror is the distance between the pole and the primary focus. It is symbolized by the letter f. The radius of curvature of small aperture spherical mirrors is found to be twice the focal length. We calculated R = 2f.

Image Formation by Spherical Mirrors 

The object’s position determines a virtual image formed by a concave mirror. Depending on the position of the object, the image is magnified, reduced, or the same size. It is discovered to be a virtual image of another position when viewed from a certain position.

Representation of Images Formed by Spherical Mirrors Using Ray Diagrams

The intersection of at least two reflected rays produces the position of the point object’s image. After reflection, a ray parallel to the principal axis will pass through the principal focus in the case of a concave mirror. A ray passing through the center of curvature of a convex mirror is reflected back along the same path. Images Formed by Spherical Mirrors Using Ray Diagrams.

Uses of Concave Mirror

Concave mirrors are commonly used to create powerful parallel beams of light in torches, searchlights, and vehicle headlights. They are frequently used as shaving mirrors to get a better view of the face. Dentists use concave mirrors to see large images of patients’ teeth.

Large concave mirrors are used in solar furnaces to concentrate sunlight and generate heat.

Uses of Convex Mirror 

Convex mirrors are commonly used in vehicles as rear-view (wing) mirrors. These mirrors are mounted on the sides of the vehicle and allow the driver to see traffic behind him or her. They also have a larger field of view because they are curved outwards. As a result, convex mirrors allow drivers to see a much larger area than a plane mirror. 

Sign Convention for Reflection by Spherical Mirrors

When dealing with a light reflection by spherical mirrors, we will use a set of sign conventions known as the New Cartesian Sign Convention. Patterns include the Spherical Mirror Reflection Sign Convention, which implies that the light from the object strikes the mirror from the left.

All distances measured perpendicular to and above the principal axis are considered positive. All distances measured to the right of the origin (along the x-axis) are positive. Distances measured perpendicular to and below the -y-axis are considered negative, while those measured below the principal axis are negative.

Mirror Formula and Magnification

In a spherical mirror, the object distance is the distance between an object and its pole (u). The image distance is the distance between the image and the mirror’s pole which is represented by  (v). The focal length is the measurement of the distance between the primary focus and the pole which is represented by (f). 

1/v 1/u = 1/f 

This formula holds true for all spherical mirrors in all positions of the object.  The magnification produced by a spherical mirror indicates the extent of an image’s image magnified in relation to the object’s height. Refraction of light is the bending of light at the interface of two different mediums. The letter m is commonly used to represent the magnification of such a mirror.

Relative Refractive Index and Absolute Refractive Index

As it travels obliquely from a denser medium to a rarer medium, a light ray bends away from the normal. A light ray bends toward the normal as it travels obliquely from a rarer to a denser medium.

In a vacuum, light travels at the incredible speed of 3108 m s-1. The speed of light varies with the medium.

The refractive index of a transparent medium is the ratio of the speed of light in a vacuum to that in the medium.

Refraction occurs at both the air-glass and the glass-air interfaces in the case of a rectangular glass slab. The incident ray is parallel to the emergent ray.

The Lens Formula and Magnification

The lens formula expresses the relationship between a spherical lens’s object distance represented by (u), image distance (v), and focal length (f).

1/v – 1/u = 1/f

Magnification

The ratio of the image’s height to the object’s height is used to determine the magnification produced by a lens, which is similar to the definition for spherical mirrors. The symbol for magnification is the letter m. If h is the object’s height and h′ is the height of the image generated by a lens, the lens’s magnification is given by,

 

M = height of the image / height of the object = h’/h

 

The object distance u and the image distance v are also connected to the lens’s magnification. This connection is made through,

M = h’/h = v/u

Power of a Lens

The power of a lens describes how much light ray convergence or divergence it can produce. The reciprocal of a lens’s focal length is known as its power. The letter P is used to symbolise it. For a lens with a focal length of f, the power P is given by,

P=1/f

The reciprocal of a lens’s focal length is its power, and Dioptre is the SI unit of lens power.

We hope these light class 10 notes will help you succeed in your exams. These class 10 light chapter notes are framed as per the CBSE textbook.