Light- Reflection and Refraction

Light- Reflection and Refraction

13.  The horizontal line passing through the centre of curvature and pole of the spherical mirror is known as Principal axis.

14.  The centre of curvature of a spherical mirror is the centre of the hollow sphere of glass, of which the spherical mirror is a part and usually represented by C.

15.  The radius of curvature of a spherical mirror is the radius of the hollow sphere of glass, of which the spherical mirror is a part and usually represented by R.

16.  The diameter of the reflecting surface that is twice the radius is called its aperture.

17.  Radius of curvature (R) = 2  focal length (f)

18.  Rules for ray diagram-

i.     The path of the reflected light ray depends upon how the incident ray is oriented with respect to the principal axis.

ii.    A ray of light parallel to the principal axis, after reflection pass through the principal focus.

iii.   A ray of light passing through the principal focus of a mirror becomes parallel to the principal axis of the mirror, on reflection

Position of object	Position of image	Size of image	Nature of image
At infinity	At focus F	Highly diminished, point – sized	Real and inverted
Beyond C	Between F and C	Diminished	Real and inverted
At C	At C	Same size	Real and inverted
Between C and F	Beyond C	Enlarge	Real and inverted
At F	At infinity	Highly enlarged	Real and inverted
Between P and F	Behind mirror	Enlarged	Virtual and erect

iv.  A ray of light incident obliquely towards the pole of mirror is reflected obliquely as per the laws of reflection

v.    A ray of light passing through centre of curvature of a mirror is reflected back along the same path

22. Image formation by a concave mirror for different positions of the object

23. Nature, position and relative size of the image formed by a convex mirror:

Position of object	Position of image	Size of image	Nature of image
At infinity	At focus F behind the mirror	Highly diminished, point	Virtual and erect
		sized
Between infinity and pole of the mirror	Between P and F behind the mirror	Diminished	Virtual and erect

24. The ratio of the height of the image to the height of the object is known as the magnification.

25. Magnification is positive for virtual image and negative for real image.

26. The phenomenon of change in the path of light from one medium to another is called refraction of light.

27. The angle formed between the incident ray and the normal is called angle of incidence and the angle formed between the refracted ray and the normal is called angle of refraction.

28. The cause of refraction is the change in the speed of light as it goes from one medium to another medium.

29. Larger the difference in speeds of light, the greater will be the angle of bending and vice-versa.

30. When a ray of light passes from a rarer medium to a denser medium, it bends towards the normal. Also, the angle of incidence is greater than the angle of refraction.