Light- Reflection and Refraction

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Introduction: Reflection and Refraction

Reflection of Light

  • The process of sending back light rays that drop on an object's surface is called Light reflection.

  • Silver metal is also one of the best light reflectors.

  • In home the mirrors we use on our dressing tables are plane mirrors..

  • A ray of light is the straight line that the light travels along and a series of light rays is considered a light beam.


Laws of Reflection of Light

  • The angle of incidence at the point of incidence is equal to the angle of reflection and the incident radius, the reflected radius and the normal mirror at the point of incidence.

  • These laws apply to all types of reflective surfaces, including spherical surfaces


Characteristics of Images Formed by Mirrors:-

  • Images created through mirrors are always virtual and erect

  • Image size is always equal to the object size, and the image is inverted laterally.

  • The images formed by the mirror on the plane are as far behind the mirror as the object facing the mirror.


Lateral Inversion: - If an object is placed in front of the mirror, left side of the object tend to be the right side of this image. This transition in an object's sides, and its mirror image, is called lateral inversion.

Spherical Mirrors

  • A circular mirror's reflective surface may be angled inside or outwards.

  • There are of two types of spherical mirrors


1. Concave Mirror: - In a concave mirror light reflection occurs at the concave surface or bent-in surface as shown in the figure below.

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2. Convex Mirror: In a convex mirror the light is reflected on the convex surface or bent out as shown in the figure below

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Commonly Used Terms about Spherical Mirrors

1. Center of Curvature: - A spherical mirror reflecting form constitutes a part of a sphere. There is a center to this sphere. This point is termed the spherical mirror's curvature center. The letter C is represented on it. Note that the curvature center isn't a part of the mirror. This exists beyond its reflective surface. Before it lies the center of curvature of a concave mirror. However, in the case of a convex mirror as shown above it lies behind the mirror.


2. Radius of Curvature: The angle of the sphere from which the reflecting surface of a spherical mirror forms a part, is considered the curvature radius of the mirror. The letter R is depicted on it.


3. Pole: - A spherical mirror's center is called its pole, and is represented by letter P as shown in figure.


4. Principle Axis: - The straight line that passes through the pole and the curvature center of a spherical mirror is called the mirror's principal axis.


Aperture of the Mirror: - Portion of the mirror from which the reflection of light actually occurs is called mirror aperture. The mirror opening actually represents mirror size.

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Principle Focus & Focal Length of a Spherical Mirrors

  • First consider the figure given below to understand the concept focus and focus length of a spherical mirror

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  • From above figure we see a set of rays landing on a concave mirror parallel to the principal axis. Now, if we observe the reflected rays, we see that they all intersect on the mirror's main axis at a point F. This feature is called the principal focus of concave mirror.

  • In the case of convex mirror rays, these reflected rays appear to originate from point F on the main axis and this point F is called the main focus of the convex mirror.

  • The distance between the pole and a spherical mirror 's principal focus is called the focal length. The letter f is represented on it.

  • There is a relationship between the curvature radius R and the focal length f of a spherical mirror and is given by R=2f, meaning that the main focus of a spherical mirror is between the pole and the curvature center.


Image Formation by Spherical Mirrors

  • The existence, direction and size of the image created by a concave mirror depend on the object's position about points P, F and C.

  • The formed picture can be both actual and simulated, depending on the object's position.

  • The picture is magnified, diminished or has the same dimension, depending on the object's position.


Rules for Obtaining Images Formed by Spherical Mirrors


Rule 1

A ray of light parallel to the mirror 's principal axis passes through its focus after mirror reflection as shown in the figure below

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From the above figure, it can be clearly seen that the light rays in concave mirrors travel through the main focus and tend to differ from the main focus in concave mirrors.

Rule 2

A ray of light that passes through the curvature center of the concave mirror or is directed towards the curvature center of a convex mirror, is reflected back along the same path as shown in the figure below.

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Rule 3

A ray going through the main focus of a concave mirror or a ray that is directed towards the main focus of a convex mirror is after reflection parallel to the main axis and is shown in the figure below.

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Rule 4

A ray incidence is projected obliquely toward the main axis, toward a point P (mirror pole), on the concave mirror, or a convex mirror. The incident and reflected rays obey the reflecting rules at the point of incidence (point P), allowing equal angles to the main axis and shown in the diagram below

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Image Formation by Concave Mirror

  • The image type created by a concave mirror depends on the position of the object stored in front of the mirror. We may place the target at the following locations

    1. Between pole P and focus F

    2. At the focus

    3. Between focus F and center of curvature C

    4. At the center of curvature

    5. Beyond center of curvature

    6. It is called infinity at far distances and cannot be shown in figures

  • The picture formed by a concave mirror for the different object locations is shown in the table below

  • Concave mirrors are used as spotlights, reflectors in car headlights, hand torches and table lights.

  • In the field of solar energy, large concave mirrors are used to focus sun rays on objects to be heated.

Image Formation by Convex Mirrors

  • To create a ray diagram, we will have to follow the direction of light rays to figure out the position, shape and scale of the image created by the convex mirror.

  • Upon reflection from the mirror, a beam of light parallel to the principal axis of a convex mirror appears to come from its centered.

  • A ray of light traveling to the center of convex mirror curvature is reflected back in its own direction.

  • Convex mirrors have their focus and curvature center behind them and no light can go behind the convex mirror and all the rays we show behind the convex mirror are virtual and no ray actually passes through the concentration and curvature center of the convex mirror.

  • Whatever the object 's position in front of the convex mirror, the convex mirror image is always behind the mirror, virtual, erect and smaller than the object..

  • In the table below is the existence, position and relative size of the image created by a convex mirror

  • Convex mirrors are used in automobiles as rear - view mirrors to see the traffic on the back side as they give erect images and also a highly decreased one that gives the wide field view of traffic behind.

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Sign Convention for Reflection by Spherical Mirrors

Spherical mirrors reflect light following a set of sign conventions called the New Cartesian Sign Convention. In this convention, the mirror's pole (P) is taken as the root. The mirror's principal axis is taken as the coordinate system's x - axis (X'X). The following are the Conventions

  • The object is always situated to the mirror's left. This implies that the light from the object falls on the left side of the mirror.

  • All distances are measured from the mirror pole parallel to the principal axis.

  • All distances measured to the right of the origin (along + x - axis) are taken as positive while those measured to the left of the origin are taken as negative (along-x-axis)..

  • Positives are taken distances measured perpendicular to and above the main axis (along y-axis).

  • Distances determined perpendicularly to and below the main axis (along -y-axis) are considered negative.

The figure below shows these new Cartesian sign conventions for spherical mirrors

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FAQs (Frequently Asked Questions)

Q1: What are Examples of Reflection and Refraction?

They see you in their head, too. This is attributed to light reflections reflecting off from you. And light hitting the eyes, is refracted and reflected.

Q2: What is the Reflection of the Light?

As light bounces off an object, reflection is. If the surface, like glass, water or polished metal, is smooth and shiny, the light will reflect at the same angle as it hits the surface. This is known as specular reflection.

Q3: What is the Difference Between Reflection and Refraction?

The fundamental difference between reflection and refraction is that light reflection is the process in which light bounces back on striking the surface, while light refraction is the process in which light changes its direction as it passes from one medium to another.

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