CLASS X SCIENCE

 The laws of reflection of light. Light –

  (i) The angle of incidence is equal to the angle of reflection, and 

(ii) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane

The laws of refraction of light.

 (i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane

. (ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. 

This law is also known as Snell’s law of refraction. 

If i is the angle of incidence and r is the angle of refraction, then, 

sini / sin  r = constant

.

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http://physicscatalyst.com/Class10/reflection_sign_convention.php

Table Showing the Sign Convention

Type of mirror	u	v		f	R	h	h of the image
		Real	Virtual				Real	Virtual
Concave mirror	-	-	+	-	-	+	-	+
Convex mirror	-	No real image	+	+	+	+	No real image	+

 Mirror Formula            1/v + 1/u = 1/f

Lens Formula              1/v - 1/u = 1/f

Power of lens             p= 1/f

For combination of  lenses  P = P1 + P2 +P3+........

Unit of power of a lens = dioptre (D)
Pole---The centre of the reflecting surface of a spherical mirror is a point called the pole
            The pole is usually represented by the letter P.

 Centre of curvature -- The reflecting surface of a spherical mirror forms a part of a 

sphere. This sphere has a centre. This point is called the centre of curvature.

 It is represented by the letter C

 Rradius of curvature   -- The radius of the sphere of which the reflecting surface of a 
              spherical mirror forms a part, is called the radius of curvature of the mirror. 
                It is represented by the letter R.

Principal axis   --A straight line passing through the pole and the centre of curvature of a spherical mirror. This line is called the principal axis. 

Principal focus of a concave mirror --A number of rays parallel to the principal axis after falling on a concave mirror meet/intersect at a point on the principal axis of the mirror. This point is called the  principal focus of the concave mirror.The principal focus is represented by the letter F.
Principal focus of the convex mirror--The reflected rays appear to come from a point on the principal axis. This point is called the principal focus of the convex mirror.
Focal length--The distance between the pole and the principal focus of a spherical mirror is called the focal length. It is represented by the letter f.

Q. What is the relationship between the radius of curvature R, and focal length f, of a spherical mirror? 
Ans: For spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length. We put this as R = 2f . 
Q. What is lateral displacement?

Ans: When a ray of light is incident obliquely on a parallel sided glass slab the emergent ray shifts laterally. The perpendicular distance between the direction of the incident ray and emergent ray is called Lateral displacement.

The factors on which the lateral displacement depends are:

Thickness of the refracting material and the refractive index of the materia

Uses of concave mirror :  
1. The dentists use concave mirrors to see large images of the teeth of patients.
2.  Large concave mirrors are used to concentrate sunlight to produce heat in solar               furnaces.
3. It is also used in torches, search-lights and vehicles headlights to get powerful parallel beams of light
Uses of convex mirror:
1.Convex mirrors are commonly used as rear-view (wing) mirrors in vehicle.Convex mirrors are preferred because they always give an erect, though diminished, image. Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view much larger area.
2. It is used to  see a full-length image of a tall building/tree in a small.