# PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction

This PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction will help you in revision during exams.

## PSEB 10th Class Science Notes Chapter 10 Light Reflection and Refraction

→ Light is an external physical agent which produces in us the sensation of sight.

→ When light travelling in one medium falls on the surface of another medium, the following three effects are observed:

• A part of the incident light is turned back (or reflected) into the first medium.
• Another part travels through the second medium along a changed path (i.e the fight is refracted).
• The remaining part is absorbed by the second medium.

→ Objects are always placed in front of the mirror to their left, so u (object distance) is always negative.

→ The focal length of the convex mirror is taken as positive (+) and that of the concave mirror as negative (-).

→ Magnification of a concave mirror forming real image is m = $$\frac{v}{u}$$ and that of convex mirror and also a concave mirror forming virtual image is m = $$\frac{-v}{u}$$.

→ All distances measured in the direction of the incident light are taken as positive and distances measured in a direction opposite to the incident ray are taken as negative.

→ The phenomenon of bending of a light ray when it travels from one medium to another medium of different optical densities is called the refraction of light.

→ When a ray of light travels from an optically rarer to an optically denser medium, it bends towards normal.

→ When a ray of light travels from an optically denser to an optically rarer medium, it bends away from normal.

→ The higher the refractive index the more is the denser medium.

→ The ratio of the sine of the angle of incidence (Sin i) to the sine of the angle of refraction (Sin r) is constant, called the refractive index of the medium.

→ The Refractive index of a medium is the ratio of the velocity of light in a vacuum to the velocity of light in a medium.

→ The lens is a portion of the transparent and refracting medium.

→ The relation between the object distance (u), the image distance (v) and the focal length (f) of a lens is called lens formula i.e. $$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$$

→ The power of a lens is the reciprocal of its focal length. Its unit is dioptre.

→ Mirror: Any smooth and polished surface is called a mirror.

→ Reflection of Light: When light falls on a mirror or a polished surface then without any change in the medium it returns into the same medium along a particular direction. This phenomenon of change of path of light is called reflection.

→ Incident Ray: A ray of light coming from a source of light falling on any surface is called an incident ray.

→ Reflected Ray: After reflection, a ray of light coming back from point of incidence into the same medium is called a reflected ray.

→ Incident Point: The point on the reflecting surface where incident ray strikes is called incident point.

→ Normal: The perpendicular drawn at the point of incidence is called normal.

→ The angle of Incidence: The angle between the incident ray and the normal is called the angle of incidence.

→ The angle of Reflection: The angle between the reflected ray and the normal is called the angle of reflection.

→ Ray of Light: The straight path of light is called a ray of light.

→ Spherical Mirror: If the mirror is a part of some hollow sphere whose one surface is polished and the other surface is reflecting then such mirror is called a spherical mirror.

→ Concave Mirror: A spherical mirror whose reflecting surface is towards the centre of a hollow sphere of which the mirror is a part, is called a concave mirror.

→ Convex Mirror: A spherical mirror whose reflecting surface is away from the centre of a sphere of which the mirror is a part, is called a convex mirror.

→ Centre of Curvature: Centre of curvature of a spherical mirror is the centre of a sphere of which the mirror is a part.

→ Pole: The midpoint of a spherical mirror is called the pole of the mirror.

→ Principal Axis: An imaginary line joining the pole and centre of curvature of a spherical mirror is called the principal axis.

→ The radius of Curvature: It is the radius of a sphere of which the spherical mirror is a part.

→ Aperture: That part of the mirror from where actually reflection takes place is called the aperture of the mirror.

→ Principal Focus: It is the point on the principal axis where the rays of light coming parallel to the principal axis after reflection actually meet or appear to diverge is called the principal focus of the mirror.

→ Focal Length: The distance between pole and principal focus of spherical mirror is called the focal length of the mirror. It is usually denoted by f.

→ Magnification: The magnification of a spherical mirror is the ratio of the length (size) of the image to the length (size) of the object. It is denoted by ‘m’.

→ Refraction of Light: The change of path of light when it goes from one medium to another medium is called refraction of light.

→ Transparent Medium: Mediums like air, water, and glass through which light can pass easily are called transparent mediums.

→ Lens: A portion of transparent and refracting medium bounded by two surfaces is called the lens.

→ Power of Lens: The capacity of a lens to converge or diverge light rays is called the power of the lens. It is denoted by ‘P’.

→ Centres of Curvature of Lens: The centres of spheres of which the spherical surfaces of the lens are part, are called centres of curvature of the lens.

→ Principal Axis of Lens: The line passing through the centres of curvature of the lens, is called the principal axis of the lens.

→ Optical Centre: A point of the lens through which rays of light go undefeated, is called an optical centre.

→ Principal Focus of Lens: The point on the principal axis of the lens, where rays coming parallel to the principal axis after refraction either actually converge or appear to diverge, is called the principal focus of the lens.