Reflection And Diffusion
Reflection rebounding of light from a polished surface.
Laws of reflection (a) I = r
(b) Incident ray, normal and reflected ray are coplanar. If the mirror is rotated by an angle θ reflected ray moves by 2θ
Diffusion reflection from a rough surface (like wall) is called diffusion. A parallel incident beam will not emerge out parallel because it meets different angles at the reflecting surface. When two mirrors are inclined at an angle θ the numbers of images are formed for an object placed in front of them.
Number of images n = 360 / θ if 360 / θ is odd and object does not lie on angle bisector or placed symmetrically n = 360 / θ - 1 if 360 / θ is odd and object placed on angle bisector or placed symmetrically.
Number of images n = 360 / θ - 1 if 360 / θ is even.
Characteristics of image formed with a plane mirror
Erect
Virtual
Size of image = size of object
Image distance = object distance (measured from mirror
Lateral inversion (left appears right and right appears left)
A, O, M, N ….X Y and so on eleven letters show lateral symmetry. When two mirrors are parallel θ = 0therefore number of images = ∞.
If the mirror is thick more than 1 image is formed and the 2nd image (formed due to first reflection from polished surface) is the brightest.
When a ray is reflected from a plane mirror angle of deviation δ = π - 2i
Minimum height of a mirror so that a person can see his full image in the mirror is half the height of the person.
Sign convention: - consider pole p as origin. All distances to its left are negative and all distances to its right are positive.
Mirror formulae: - 1 / v + 1/u = 1 /f f= R/ 2
Where
V = image distance from pole to the mirror
U = object distance from pole to the mirror
F = focal length
R = radius of curvature
| Real image |
Virtual image |
| Rays actually converge to form image |
Rays appear to diverge |
| Image is inverted |
Image is erect |
| Can be obtained on screen |
Cannot be obtained on screen |
| Magnification is negative |
Magnification is positive |
Magnification (lateral):- M lat = - v / u = I / O
M lat = v –f / f = f / u – f
Lens makers formula when surrounding medium is air is
Magnification (axial) m axial = 0 (v2/u2) (valid for small objects)
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