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 | |
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.