Light: Reflection and Refraction Class 10

Nature of Light:

1. Particle Nature 

2. Ray Nature 

Bean of Light 

Bunch of rays is called beam of light 

Types of Beam

Reflection of Light

Reflection - The bouncing back of a particle or wave that strikes the boundary between two media.

Law of Reflection - 

1. The angle of incidence equals the angle of reflection.

2. Incident rays and reflected rays make equal angles with a line perpendicular to the reflecting surface, called the normal.

Specular or Regular Reflection -

This occurs when parallel rays of light hit a smooth surface.

All the light rays reflect at the same angle because of the smooth surface. So you can see a clear image.

The reflection of wave in one direction from a smooth surface.

Diffuse Reflection - The reflection of waves in many directions from a rough surface.

Each ray obeys the law of reflection.

What are Mirrors?

A mirror is an object with a surface that has good specular reflection, able to produce an image.

A surface capable of reflecting sufficient diffused light to form an image of an object placed in front of it.

Plane (flat) Mirrors can only produce virtual images.

Virtual Image - An image formed from light rays that only appear to be coming from behind the reflecting surface. This image cannot be obtained on a screen.

Characteristics of Images in Plane Mirror

1. Image located as far into the mirror as object is in front of mirror.

2. Virtual Image

3. Erect Image

4. Same Size

5. Lateral Inversion (Reverse left to right(

6. Image form directly in front of object.

What are Spherical Mirrors?

Spherical Mirror is a cut part of a hollow glass sphere, such that one of its sides has been polished, and so the other side reflects the light falling on its surface.

Concave and convex mirrors shown as part of complete hollow sphere.

Here are the definitions of the terms related to a concave mirror:

1. Pole 

The pole is the geometrical center of the reflecting surface of the concave mirror. It is usually denoted by the letter P.

2. Principal Axis

The principal axis is the straight line that passes through the pole and the center of curvature of the mirror. It is perpendicular to the surface of the mirror at the pole.

3. Centre of Curvature

The centre of curvature is the center of the sphere from which the concave mirror is a part. It lies in front of the mirror and is denoted by the letter C.

4. Focus (Principal Focus)

The focus of a concave mirror is the point on the principal axis where parallel rays of light (parallel to the principal axis) converge after reflection. It is denoted by the letter F.

5. Radius of Curvature

The radius of curvature is the distance between the pole (P) and the centre of curvature (C) of the mirror. It is denoted by the letter R.

6. Focal Length

The focal length is the distance between the pole (P) and the focus (F) of the mirror. It is denoted by the letter f.

For a concave mirror:

f = R/2

Rules to Draw Ray Diagram 

There are some rules which we use to obtain images in a ray diagram Let's look at them

Rule 1 - Ray parallel to principal axis will pass through focus after reflection..

Rule 2 - Ray passing through focus will become parallel to principal axis after reflection.

Rule 3 - Ray passing through Center of Curvature will follow the same path back after reflection

Rule 4 - Ray incident at pole is reflected back making same angle with principal axis.

Applications of Concave Mirrors

Used in shaving mirrors: 

Converging mirrors are most widely used in shaving because they have reflective and curved surfaces. At the time of shaving, the concave mirror forms an enlarged as well as erect image of the face when the concave mirror is held closer to the face.

The concave mirror used in the ophthalmoscope: These mirrors are used in optical instruments as in ophthalmoscopes for treatment.

Uses of the concave mirrors in astronomical telescopes: 

These mirrors are also widely used in making astronomical telescopes. In an astronomical telescope, a converging mirror of a diameter of about 5 meters or more is used as the objective.

Concave mirrors used in the headlights of vehicles: 

Converging mirrors are widely used in the headlights of automobiles and in motor vehicles, torchlight, railway engines, as reflectors. The point light source is kept at the focus of the mirror, so after reflection, the light rays travel over a huge distance as parallel light beams of high intensity.

Used in solar furnaces: 

Large converging mirrors are used to focus the sunlight to produce heat in the solar furnace. They are often used in solar ovens to gather a large amount of solar energy in the focus of the concave mirror for heating, cooking, melting metals.

Image Formed by Concave Mirror 

1. When object is at infinity.

Position of Image: At focus

Size of Image: Highly diminished 

Nature of Image: Real and inverted 

2. When object is beyond 'C' (centre of curvature)

Position of Image: Between C and F

Size of Image: Diminished (smaller than object)

Nature of Image: Real and inverted 

3. When object is at 'C' (centre of curvature)

Position of Image: At 'C' ( centre of curvature)

Size of Image: Equal in size of object (same size of object)

Nature of Image: Real and inverted 

4. When object is between 'C' and 'F'

Position of Image: Beyond 'C' ( centre of curvature)

Size of Image: Enlarged ( bigger than object)

Nature of Image: Real and inverted 

5. When object is at 'F' (focus).

Position of Image: At infinity 

Size of Image: Highly Enlarged 

Nature of Image: Real and inverted 

6. When object is between 'F' ( focus) and 'P' (pole).

Position of Image: Behind the mirror 

Size of Image: Enlarged 

Nature of Image: Virtual and Erect 

CONVEX MIRROR 

Rules to Draw Ray Diagram 

Rule 1

For concave mirror: A ray of light parallel to the principal axis will pass through the focus after reflection.

          Concave Mirror.               Convex Mirror 

For Convex mirror: A ray of light parallel to the principal axis will appear to come from focus.

Rule 2

For concave mirror: A ray passing through the principal focus(F) becomes parallel to the principal axis.

          Concave Mirror.               Convex Mirror 

For convex mirror: A ray directed towards principal focus becomes parallel to the principal axis.

Rule 3

For Concave mirror: A ray passing through the centre of curvature will take the same path after reflection.

         Concave Mirror.                 Convex Mirror 

For convex mirror: A ray directed towards the centre of curvature will take the same path after reflection

Rule 4

For any ray incident at any angle at the pole(P), the reflected ray follows the law of reflection for both concave as well as convex mirrors.

          Concave Mirror.                Convex Mirror 

Uses of Convex Mirrors

1. Rearview Mirrors in Vehicles: Convex mirrors are often used as rearview mirrors in vehicles. These curved mirrors help drivers see more of what’s behind them, making it easier to check for blind spots and see a bigger area. This makes driving safer and helps stop accidents from happening.

2. Security and Surveillance: Arched mirrors are regularly utilized in security and observation frameworks. Their capacity to supply a wide, all encompassing see makes them perfect for observing ranges where comprehensive perception is pivotal, such as in stores, shopping shopping centers, stopping parts, and other open spaces.

3. Stores and Retail Outlets: In stores, general stores, and retail outlets, raised mirrors are deliberately put to empower workers to watch different walkways or corners from a single vantage point. This makes a difference anticipate robbery, shoplifting, and guarantees superior client help.

4. Street Security: Raised mirrors are utilized on streets, particularly at convergences and sharp twists, to improve perceivability for drivers. These mirrors permit drivers to expect oncoming activity or people on foot, in this way decreasing the probability of mishaps.

Image formation by convex mirror 

1. Whenever the object is positioned at infinity, a virtual, upright, substantially decreased, and point size picture is generated behind the mirror at the focus.

2. When the object is put at a limited distance from the convex mirror, a virtual, reduced, and erect image is generated between the focus of the convex mirror and the pole.

NEW CARTESIAN CONVENTION

Reference Point: All distances are measured from the pole (center) of the mirror, which acts as the origin (0,0) in a coordinate system. 

Direction of Incident Light: The direction of the incoming light is considered the positive direction. 

Object Distance (u): The distance between the object and the pole is always negative for real objects placed in front of the mirror. 

Image Distance (v): The distance between the image and the pole. It's positive for virtual images (formed behind the mirror) and negative for real images (formed in front of the mirror). 

Focal Length (f): The distance between the pole and the focal point. It's positive for convex mirrors and negative for concave mirrors. 

Height of Object (h): Always considered positive as the object is typically placed above the principal axis. 

Height of Image (h'): Positive for erect images and negative for inverted images. 

A convex lens, also known as a converging lens, is thicker at the center and thinner at the edges. It converges parallel rays of light to a single point called the focus (F). This ability to converge light makes convex lenses essential in various optical devices. 

The type, size, and nature of the image formed by a convex lens depend on the object's position relative to the lens and its focal point. 

Here's a breakdown of image formation for different object positions:

Object at Infinity: The image is formed at the focal point (F) on the opposite side of the lens.

Nature: Real and inverted.

Size: Highly diminished (point-sized

When an object is placed beyond the centre of curvature, the real image is formed between the centre of curvature and focus. The image size will not be the same as the object. It will be diminished in size

When an object is at the centre of curvature, the real image is formed at the other centre of curvature. The size of the image is the same as compared to that of the object.

When an object is placed in between the centre of curvature and focus, the real image is formed behind the centre of curvature. The size of the image is larger than that of the object.

When an object is placed at the focus, a real image is formed at infinity. The size of the image is much larger than that of the object.

When an object is placed in between focus and optical centre, a virtual image is formed. The size of the image is larger than that of the object.