CBSE Class 10 Science Revision Notes Chapter 10

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

Understanding every concept from the NCERT Books is essential to scoring well in the 10th board examination. As the course and curriculum of Class 10 are very vast, it becomes very challenging for students to cover it and later revise it. With so many subjects to cover, Science is among the tough ones to crack. Hence, Extramarks has provided CBSE Class 10 Science Revision Notes Chapter 10 on its website. Students can easily find all the revision notes chapter-wise. The experts have developed these notes adhering to the CBSE and NCERT guidelines. They can even refer to the detailed CBSE Class 10 Science Revision Notes Chapter 10 – Light Reflection and Refraction. Extramarks has also provided CBSE Previous Year Question Papers, CBSE Extra Questions, Formula, Answer keys, etc on its website. 

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

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Introduction

An object reflects light that falls on its surface. Our eyes utilise reflected light to see the world around us. Since light can pass through transparent objects, we are able to see through them. The generation of images in mirrors, the twinkling of stars, the stunning colours of a rainbow, the bending of light by materials, and many more common and spectacular phenomena are all related to light. We can learn more about light’s characteristics by studying them. We can infer that light appears to move in straight lines by looking at the common optical phenomena we encounter every day. This straight-line path of light, which is typically represented as a ray of light, is demonstrated by the fact that a small source of light casts a sharp shadow on an opaque object.

Using the straight-line propagation of light, we will examine the reflection and refraction of light phenomena in this chapter. We can explore several optical phenomena in nature with the guidance of these fundamental ideas. In this chapter, we’ll try to comprehend how light is reflected by spherical mirrors, refracted, and used in practical applications.

Important Terms

• Light is an energy source that can be turned into various forms of energy.
• Light does not need a physical medium to travel.
• The velocity of light in air or vacuum is 3*10^8 m/s.

Rectilinear Propagation of Light

Inside a homogeneous transparent material, light travels in a straight path, which is known as rectilinear propagation of light.

Reflection of Light

The phenomenon of light reflection illustrates how a beam of light alters its propagation direction when it hits a barrier between two media through which it cannot flow. 

There are further two types of reflection of light: 

Regular Reflection

Specular or regular reflection is the flawless, mirror-like reflection of light. Reflections on mirrors, water surfaces, and highly polished floors are examples of regular reflections.

Irregular Reflection

When a light ray contacts a rough or unpolished wall or wood, it causes irregular reflection, also known as dispersed reflection. The incident light is reflected in different directions by distinct sections of the surface in this scenario. No definitive picture is generated in such circumstances, but the surface becomes apparent. It is usually known as light scattering. Non-luminous objects become apparent as a consequence of the dispersed reflection.

Reflection of Light by a Plane Surface:

Make an illustration. Follow the below-mentioned points to understand it better. 

• Consider MM’ to be a reflective surface. 
• A light beam that strikes MM’ in the direction IO is reflected in the direction OR. 
• IO represents the incident ray, O represents the point of incidence, and OR represents the reflected ray.
• Let ON be the normal perpendicular to the surface MM’ at the point of incidence. 
• The angle of incidence, designated by the symbol I, is the angle produced at the point of incidence by the incident ray and the normal. 
• The angle of reflection ‘r’ is the angle created at the point of incidence by the reflected ray and the normal. 
• A reflecting surface is similar to a mirror.

Laws of Reflection:

The rules of reflection are seen to apply to the reflection of any planar surface. According to the equations of reflection, the incident ray, reflected ray and regular at the point of incidence all reside in the same plane. The incidence angle equals the reflection angle.

Nature of Image Formed By a Plane Reflecting Surface:

An image might be real or virtual. A real picture is generated when light rays connect after reflection. A virtual picture is generated when the light beams after reflection do not indeed intersect but appear to deviate from it (these rays of light intersect when produced backwards).

Ray Diagrams of Plane Mirrors:

When designing ray diagrams, the following rays are frequently considered: 

• A light beam incident at 90 degrees on a flat mirror is reflected back along the same path. 
• A beam of light striking a flat mirror at any angle is reflected in such a way that the angle of incidence equals the angle of reflection. 
• When the reflected rays appear to collide, a picture is generated.

Spherical Mirrors:

A spherical mirror is a mirror with a polished, reflecting surface that is part of a glass or a plastic hollow sphere. A tiny layer of silver is applied to one of the two curving surfaces of a spherical mirror, followed by a coat of red lead oxide paint. As a result, one side of the spherical mirror is opaque, while the other is highly polished.

Based on the characteristics of its reflecting surface, the spherical mirror is classed as follows:

Concave Mirror

A concave mirror is a spherical mirror with its reflecting surface pointed toward the sphere’s centre.

Formation of Image by a Concave Mirror

Convex Mirror

A convex mirror is a spherical mirror with an inclined reflecting surface away from the centre of the sphere it is a part of.

Formation of Image in a Convex Mirror

Mirror Formula

• In a spherical mirror, the distance of the object from its pole is called the object distance (u). 
• The distance of the image from the pole of the mirror is called the image distance (v). 
• You already know that the distance of the principal focus from the pole is called the focal length (f). 
• There is a relationship between these three quantities given by the mirror formula which is expressed as 1/v + 1/u = 1/f. 

This formula is valid for all spherical mirrors at all positions of the item. To solve difficulties, you must apply the New Cartesian Sign Convention when substituting numerical values for u, v, f, and R in the mirror formula.

Magnification

The magnification generated by a spherical mirror indicates the amount to which an item’s image is enlarged in relation to the object’s size. It is defined as the ratio of the image’s height to the object’s height. The letter m is commonly used to symbolise it. If h is the object’s height and h′ is the image’s height, then the magnification m generated by a spherical mirror is given by:

M = Height of the image/ Height of the object 

Laws of Refraction

(i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence lie in the same plane. 

(ii) In the law of refraction, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for the light of a given colour and the given pair of media. It is also called Snell’s law of refraction. (This is true for angle 0 < i < 90 degrees) If i is the angle of incidence and r is the angle of refraction. 

Refraction of Light through a Glass Slab

• In this aActivity, you will note that the light ray has changed its direction points O and O′. 
• Note that both the points O and O′ lie on surfaces separating two transparent media. 
• Draw a perpendicular NN’ to AB at O and another perpendicular MM′ to CD at O′. 
• The light ray at point O has entered from a rarer medium to a denser medium, that is, from air to glass. 
• Note that the light ray has bent towards the normal. 
• At O′, the light ray has entered from glass to air, that is, from a denser medium to a rarer medium. 
• The light here has bent away from the normal. 
• Compare the incidence angle with the refraction angle at both refracting surfaces AB and CD.
• In the figure above, a ray EO is obliquely incident on surface AB, called an incident ray.
• OO′ is the refracted ray, and O′ H is the emergent ray. 
• You may observe that the emergent ray is parallel to the direction of the incident ray. 
• The extent of bending of the ray of light at the opposite parallel faces AB (air-glass interface) and CD (glass-air interface) of the rectangular glass slab is equal and opposite. 
• This is why the ray emerges parallel to the incident ray.
• However, the light ray is shifted sideward slightly. 

Lenses

A lens is a transparent refracting media section defined by two commonly spherical or cylindrical surfaces, or one curved and one flat surface. The two types of lenses are convex lenses and converging lenses.

Terminology Used in Optics

• Optical Centre: It is a lens’s focal point. It is symbolised by the letter O. A ray of light does not deviate as it passes through the optical centre of a lens. It is also referred to as an optic centre.
• Principal Axis: The primary axis is the straight line that links the curvature centres of the two curved surfaces of a lens.
• Principal Foci: Since light rays can flow through the lens in either direction, there will be two primary foci on either side of the lens, known as the first and second principle foci of a lens, correspondingly.
• First Principal Focus (F1): After refraction from the lens’s two surfaces, it is a point on the lens’s principal axis where light rays emanating from it (convex lens) or seeming to meet at the point (concave lens) become parallel to the lens’s principal axis.
• Second Principal Focus (F2): It is a point on the lens’s primary axis at which light rays parallel to the lens’s principal axis after refraction pass through (convex lens) or appear to emerge from the concave lens.

Formation of Image by a Concave Lens

Uses of Concave Lens

• Concave mirrors often create intense parallel beams of light in torches, searchlights, and vehicle headlights. 
• They are frequently used as shaving mirrors to view the face better. 
• Dentists utilise concave mirrors to see vast pictures of patients’ teeth. 
• Large concave mirrors are used in solar furnaces to focus sunlight and generate heat.

Sign Convention for Lenses

All distances are measured from the optical centre of the lens. Distances measured in the incident light’s direction are regarded as positive, whereas distances measured in the opposite direction are considered negative. All measurements made above the primary axis are regarded as positive, whereas measurements taken below the principal axis are considered negative; hence, object height is always positive, but image height is only positive for virtual images

Lens Formula

The lens formula, also known as the lens equation, defines the relationship between the object’s distance (u), the image’s distance (v), and the lens’s focal length (f).

1/F = 1/V – 1/U 

Power of a Lens

When a beam of light goes through a lens, it bends (except when it passes through the optical centre). The bending of light rays towards the major axis is known as convergence, while the bending of light rays away from the principal axis is known as divergence. A lens’s power reflects its degree of convergence or divergence. A small focal length lens deviates the rays more than a large focal length lens. As a result, the power of a lens is defined as the reciprocal of its focal length measured in metres.

Power of a lens = 1/ Focal length in metres 

Dispersion and Scattering of Light

Light dispersion is a phenomenon that occurs when white light travels through material and splits into seven distinct hues. Various hues are known to move at different rates.

Scattering of Light

Scattering is a generic physical phenomenon that causes some forms of radiation, such as light or moving particles, to deviate from a straight course due to one or more localised non-uniformities in the material through which they travel.

Tyndall Effect

The Tyndall Effect is basically a phenomenon or a process wherein light rays direct in a colloid scatter at cells. This effect is exhibited by fine suspensions and colloidal fluids. Thereafter, it can be utilised to understand whether the given solution is colloidal or not. The intensity of scattered light is affected by both the density of colloidal particles and input light frequency

Notes of Physics Class 10 Chapter Light Reflection and Refraction

Here is a glimpse of a summary of Class 10 Science Chapter 10 Notes. 

• • Light seems to move in straight lines.
  • Object images are formed by mirrors and lenses. Depending on the item’s location, images might be real or virtual.
  • The rules of reflection apply to all sorts of reflecting surfaces. The refracting surfaces follow the rules of refraction.
  • For spherical mirrors and lenses, new Cartesian Sign Conventions are used.
  • A spherical mirror’s focal length equals half its curvature radius.
  • The magnification generated by a spherical mirror is the image height ratio to the object height.

• A light beam bends away from the normal as it travels obliquely from a denser medium to a rarer media. A light beam travels obliquely from the source and bends towards the normal.

Class 10 Chapter 10 Science Notes – Light

Light and Reflection Class 10 Notes – Mirrors

Class 10 Science Chapter Light Reflection and Refraction Note – Refraction