Law of reflection
- The incident ray , the normal and the reflected ray at the point of incidence , all lie on the same plane .
- The angle of incidence is equal to the angle of reflection .
plane mirror
Characteristics of Image formed in a Plane Mirror
(i) laterally inverted
(ii) image is virtual
(iii) image is same size as the image
(iv) image distance same as object distance
(v) upright
Curved Mirrors
- C = centre of curvature
- r = radius of curvature
- P = pole
- PC = principle axis
Effect of curved mirrors on incident rays :
a) Incident rays parallel to the principal axis
- Rays parallel to the principal axis converge at the principal focus , F .
- F is positioned at the midpoint between C and P .
- FP is named the focal length which is denoted by f .
b) Incident rays parallel to each other but not parallel to the principal axis
- Parallel rays converge at a point called secondary focus
- The focal plane joins F , the principal focus and all secondary foci and is perpendicular to the principal axis .
- The ray passing through C is reflected back along the line of the incident ray .
- The distance between the focal plane and the mirror is the focal length , f .
Application
(I) Plane Mirror
Plane mirror in an electrical meter to avoid parallax error .
Instrument for checking teeth .
(II) Concave Mirror
Light reflector in a torchlight .
The reflecting telescope .
(III) Convex Mirror
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