Light: Reflection and Refraction- Revision Notes

Light: Reflection and Refraction is the 10^th chapter of class 10^th CBSE science. In this article, we have provided you with quick revision notes for this chapter. It covers important topics such as reflection of light, refraction of light, refractive index, spherical mirrors, sign convention in spherical mirrors, mirror formula, lens and image formation by lens. Since the topics are discussed only briefly here, to get more detailed notes on each topic in this chapter, Click Here

Read Also: Lens Formula and Magnification

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Types of Spherical Mirrors

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• Convex mirror: This mirror has a convex reflecting surface. It is also known as a diverging mirror since it diverges the light.

• Concave mirror: The reflecting surface of this mirror is concave. It is also known as a converging mirror since it converges the light.

• Concave mirrors are used as a cosmetic mirror, a reflector in torches, automobile and searchlight headlamps, doctor's head-mirrors, solar furnaces, and other applications. On the other hand, Convex mirrors are utilized as rearview mirrors in automobiles, shop security mirrors, and other applications.

    

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Terms Related to Spherical Mirrors

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• The center of a hollow sphere, of which the mirror is a component, is called the center of curvature.

• The radius of curvature is the diameter of the hollow sphere in which the mirror is embedded.

• Pole is the mirror's center (middle point).
• The main axis is the line that connects the pole with the center of curvature.
• Aperture refers to the size of a mirror.
• The point on the primary axis where all incident rays parallel to the principal axis converge or diverge after reflection via a mirror is known as the principal focus.
• The focal length is the distance between the pole and the focus point.

Read More About Image Formation by Lenses

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Spherical Mirror Sign Conventions

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• All distances are calculated using the mirror's pole as the origin.

• Positive distances are those measured in the direction of incident rays.

• Negative distances are those measured in the opposite direction of incoming rays.
• Positive distances are those measured upward and perpendicular to the main axis.
• Negative distances are measured downhill and perpendicular to the main axis.

Read More About Refraction by Spherical Lenses

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Mirror Formula & Magnification

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The mirror formula is given below:

\({1\over f} = {{1\over v} +{1\over u}}\)

where f, v, and u stand for focal length, image distance, and object distance, respectively.

The ratio of the image's height to the object's height is known as linear magnification. The formula for magnification is given below:

\(m = {h'\over h}\)

where m = magnification, h = image height, and h' = object height

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Refraction

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

• When the velocity of light in a medium is higher, it is referred to as optically rarer.

• Air or vacuum, for example, is more optically uncommon.

• When the velocity of light in a medium is lower, it is said to be optically denser.
• Glass, for example, has a higher density than air.

Read More About Refraction of Light

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Refractive Index 

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The degree or extent of bending of light when it travels from one medium to another is measured by the refractive index.

The refractive index is divided into two types: relative and absolute.

• The relative Refractive Index is the refractive index of a media in relation to another medium.
• Refractive index of medium 1 in relation to medium 2 = Speed of light in medium 2(V₂)/Speed of light in medium 1(V₁)
• Absolute Refractive Index is the refractive index of a medium with relation to air or vacuum.
• Absolute refractive index of medium (m) = Speed of light in air(c)/Speed of light in medium(V_m)

Refracted Ray: The outgoing beam from the refracting surface is called a refracted ray.

• The angle between incident rays and the perpendicular line (normal) at the site of incidence is called an angle of incidence (I).

• The angle between refracted rays and the perpendicular line (normal) at the moment of incidence is called an angle of refraction (r).

The Law of Refraction is a set of rules that governs how light is reflected.

• “At the point of incidence, the incident ray, refracted ray, and normal all lie in the same plane.”
• “The sine of the angle of incidence is proportional to the sine of the angle of refraction.”
•  \({sin(i)\over sin(r) } = Constant\)

Read More:

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Lens

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The transparent refracting medium limited by two surfaces, at least one of which is curved, is referred to as a lens.

There are two types of lenses: 

• Convex lens
• Concave lens

Image Formation by Lens: Special Rays

• After refraction, an incident ray parallel to the main axis travels through (or seems to emanate from) the lens' second focus.

• An incident ray that passes through the lens' optical center does not deviate from the lens.

• After refraction via the lens, an incoming ray traveling through or directed toward the (first) primary focus becomes parallel to the principal axis.

Use of Lens

Photographic cameras, magnifying glasses, microscopes, telescopes, and the human eye all use lenses.

1. Light follows a straight path.

2. When light strikes polished surfaces, such as mirrors, it is reflected.

3. When light moves from one medium to another, it is refracted.
4. There has been a shift in wavelengths!

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Some important Points to Remember

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• Light bouncing back when it strikes a smooth or polished surface is referred to as reflection. There are two forms of reflection: specular or regular reflection and diffuse or irregular reflection.
• The incidence angle is the same as the reflection angle. I = r is the mathematical formula.
• The picture is upright, imaginary, and unmagnified.
• The picture is reversed from right to left.
• A planar mirror's focal length is infinite.
• A planar mirror has no power.
• The reflected ray rotates by 2 when a plane mirror is rotated at an angle.
• The smallest plane mirror that may be used to observe an item is half the size of the object.
• Pole (Vertex): The pole of a mirror is its center point.
• Focal plane: A plane that passes through the primary focus and is drawn perpendicular to the major axis.
• Focal length: The focal length is the distance between the pole and the focus. It is symbolized by the letter f. The focal length is half the curvature radius.
• Aperture: The aperture refers to the size of the mirror. It's also known as the effective diameter of the mirror's light-reflecting region.
• Genuine image: When light beams intersect at a location following reflection from a mirror, the picture created by these rays is said to be real. On a screen, real pictures may be obtained.
• Virtual image: When light beams appear to intersect at a location following reflection from a mirror, the picture created by these rays is said to be virtual. On a screen, virtual pictures are impossible to obtain.
• When creating ray diagrams to locate the location of a picture, the following points should be noted:

1. After reflection, a beam of light parallel to the primary axis passes through the focus.
2. After reflection, a beam of light traveling through the focus becomes parallel to the primary axis.
3. After reflection in the mirror, a beam of light incident on the center of curvature retraces its course.

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