Page 101 - Light

 Contact for Notes , Objective , Subjective Questions & Answers of any Subject - किसी भी विषय के नोट्स, वस्तुनिष्ठ, दीर्घ प्रश्न व उत्तर के लिए संपर्क करें - ₹35/Subject

 Click here for Hindi Medium

Light :- Reflection of light

• Light :- Light is a form of energy, which enables us to see an object.

Note:-
(i) Light is an electromagnetic wave.
(ii) Light always travels in a straight line.

• Ray of Light: - The straight line path of light traveling in any direction is called a ray of light.

• Beam of Rays :- A group of rays of light in a certain direction is called a beam.

There are three types of beams -

1. Parallel Beam of Rays
2. Convergent Beam of Rays
3. Divergent Beam of Rays

1. Parallel beam: - Such a beam in which all the rays are parallel to each other is called a parallel beam.

2. Converging beam: - Such a beam in which all the rays meet at a point is called a convergent beam.

3. Diverging beam: - Such a beam in which all the rays appear to be scattered from a single point is called a diverging beam.

• Shadow:- When an opaque object is placed on the path of light, the light does not pass through that opaque object, so a dark area is formed there which is called shadow.

• Mirror :- That piece of a substance is called a mirror which is a relief surrounded by two surfaces. Out of which one surface remains clean and the other remains polished.

There are two types of mirrors

1. Plane Mirror
2. Spherical Mirror

1. Plane mirror: - That mirror is called a plane mirror, both the surfaces of which are flat, out of which one surface is polished.

2. Spherical mirrors: - Spherical mirrors are called that which is a section of a hollow sphere, in which one of the two surfaces that are pressed down or raised up remains clean and the other is polished.

**

There are two types of Spherical mirrors.
1. Concave Mirror
2. Convex Mirror

1. Concave mirror:- Such a spherical mirror in which light is reflected from the surface pressed down, it is called concave mirror.

 2. Convex mirror: - Such a spherical mirror in which light is reflected from the raised surface is called a convex mirror.

• Reflection of light: - When a ray of light falls on a reflective surface and returns to the same medium, then this process is called reflection of light.

• Laws of reflection of light: - The rules by which a ray of light falls on a surface and gets reflected, those rules are called the laws of reflection of light.

# Reflection of light in a plane mirror

1. Point of incidence: - The point on the mirror where the incident ray falls is called the point of incidence.

2. Incident ray: - The ray of light which is reflected on the mirror is called incident ray.

3. Reflected ray: - The ray of light which is returning after colliding with the mirror is called reflected ray.

4. Normal :- The normal drawn at the point of incidence of a mirror is called the normal of that mirror.

5. Angle of incidence :- The angle formed by the incident ray and the normal at the point of incidence is called the angle of incidence.

6. Reflected angle: - The angle formed by the reflected ray and the normal at the point of incidence is called the reflected angle.

# laws of reflection of light

There are two laws of reflection of light.

1. The incident ray, the reflected ray and the normal at the point of incidence all fall in the same plane.
2. The angle of incidence is equal to the angle of reflection.

That is, ㄥi = ㄥr

***

• What is image?
Answer :- The point at which the rays of light coming from an object point intersect or appear to intersect after being reflected or refracted is called the image of that object.

# types of image 

(i) Real Image

(ii) Virtual Image

(i) Real Image:- Such an image which is formed by the actual meeting of reflected or refracted rays is called real image.


(ii) Imaginary Image / Virtual Image :- Such an image which is formed by virtual intersection of reflected or refracted rays is called imaginary image.


# Difference between imaginary and real image

Virtual Image	Real Image
1. This image is formed by the virtual intersection of the reflected or refracted rays. 2.This image is always erect. 3. This image cannot be shown on the screen. 4. It formed back on the mirror. 5. It is formed in front of the lens.	1. This image is formed by the actual intersection of the reflected or refracted rays. 2. This image is always inverted. 3. This image can be shown on the screen. 4. It formed forward on the mirror. 5. It formed over the lens behind it.

-----

• Parts of Spherical Mirror

(i) Pole

(ii) Principal Axis

(iii) Focus 

(iv) Center of curvature

(v) Focal Length

(vi) Radius of Curvature

(vii) Aperture

** **

(i) Pole:- The center point of the reflecting surface of a spherical mirror is called the pole of that spherical mirror.

P is the pole.

(ii) Principal Axis :- The line passing through the pole and center of curvature of a spherical mirror is called the principal axis of that mirror.

PX is the principal axis.

(iii) Focus :- The point at which the rays of light coming parallel to the main axis of a spherical mirror converge or appear scattered after reflection is called focus.

F is the focus.

The focus is denoted by 'F'.

(iv) Center of curvature:- The center of the hollow sphere whose segment is a spherical mirror is called the center of curvature of that spherical mirror.

C is the center of curvature.

The center of curvature is denoted by 'C'.

(v) Focal Length :- The distance between the pole and the focus of a spherical mirror is called focal length.

PF is the focal length.

The focal length is denoted by 'f'.

(vi) Radius of Curvature:- The distance between the pole and the center of curvature of a spherical mirror is called radius of curvature.

PC is the radius of curvature.

The radius of curvature is denoted by r or R.

(vii) Aperture :- The width of a spherical mirror is called the aperture of that spherical mirror.

**  *  **

• What is Lens /?

Answer:- That piece of transparent medium is called lens which is surrounded by two surfaces. Out of which one surface is definitely crooked.

#There are two types of lens -

(i) Concave lens

(ii) Convex lens

(i) Concave lens: - A lens whose thickness is least in the middle and maximum at the edges is called a concave lens.

(ii) Convex lens: - A lens whose thickness is maximum in the middle and minimum at the edges is called a convex lens.

**  **  **
• Why is a convex lens called a convex lens?
Answer :- The rays of light falling on a convex lens meet at a point after refraction. That's why a convex lens is called a virtual lens.

• Why is a concave lens called a diverging lens?
Answer :- Rays of light falling on a concave lens appear scattered from a point after refraction. That's why concave lens is called diverging lens.

Parts of the Lens
1. Principle Axis of Lens 
2. Light Centre / Optical Centre 
3.  Focus of Lens 
4. Focus of lens 
5.  Focal length of lens 
6.  Radius of Curvature of lens 
7.  Aperture of lens 

** ** ** *

1. Principle Axis of Lens :- The line passing through the center of curvature of the lens is called the principal axis of the lens.

2. Light Centre/Optical Centre:- The light center of a lens is the point located inside it on the principal axis, passing through which the rays of light are refracted without bending.

3. Focus / nucleus of the lens: - The point at which the rays of light coming parallel to the principal axis of the lens meet after refraction or the point from which they appear scattered, is called the focus of the lens. It is said

The focus of the lens is denoted by "F".

4. Center of curvature of the lens :- The centers of the two spheres of which the lens is a part are called the centers of curvature of the lens.

5. Focal length of lens: - The distance between the center of light and the focus of the lens is called focal length.

6. Radius of Curvature of lens:- The distance between the center of light and the center of curvature of the lens is called the radius of curvature of the lens.

7. Aperture of lens:- The diameter of the circular circumference of a lens is called the aperture of that lens.

** ** ** **

Sign Convention

In a spherical mirror or lens, sometimes the image is formed in front of it and sometimes behind it. In these circumstances, the convention (law) by which the difference is made clear is called the Sing convention.

Co-ordinate sign convention is prevalent nowadays.

according to coordinate Sign convention

1. The object is placed to the left of the mirror or lens.

2. Object distance (u), image distance (v) and focal length (f) are measured from the pole of the mirror and the optical center of the lens.

3. The distance above the principal axis is positive ( + ) and the distance below is negative ( - ).

4. The distance from pole and light center to the left is negative (-) and to the right is positive (+).

conclusion

1. The object distance is always negative (-) in any mirror or lens.

2. The focus of a convex lens and a convex mirror is always positive.

3. The focus of concave lens and concave mirror is always negative (-).

4. When a real image is formed in a lens, the image distance is positive (+) and when an imaginary image is formed, the image distance is negative (-).

5. When a real image is formed in a mirror, the image distance is negative (-) and when an imaginary image is formed, the image distance is positive (+).

👉Click here for numerical questions

The  End