Image Formation by Plane Mirror
| Object Position | Image Position | Nature | Size |
|---|
| Anywhere in front | Same distance behind mirror | Virtual & erect | Same as object |
Image Formation by Concave Mirror
| Object Position | Image Position | Nature | Size |
|---|
| At infinity | At focus (F) | Real, inverted | Highly diminished |
| Beyond centre of curvature (C) | Between C and F | Real, inverted | Diminished |
| At centre of curvature (C) | At C | Real, inverted | Same size |
| Between C and F | Beyond C | Real, inverted | Enlarged |
| At focus (F) | At infinity | Real, inverted | Highly enlarged |
| Between F and pole (P) | Behind mirror | Virtual, erect | Enlarged |
Image Formation by Convex Mirror
| Object Position | Image Position | Nature | Size |
|---|
| At infinity | At focus behind mirror | Virtual, erect | Highly diminished |
| Anywhere in front | Between pole and focus | Virtual, erect | Diminished |
Image Formation by Convex Lens
| Object Position | Image Position | Nature | Size |
|---|
| At infinity | At focus on other side | Real, inverted | Highly diminished |
| Beyond 2F | Between F and 2F | Real, inverted | Diminished |
| At 2F | At 2F | Real, inverted | Same size |
| Between F and 2F | Beyond 2F | Real, inverted | Enlarged |
| At focus (F) | At infinity | Real, inverted | Highly enlarged |
| Between lens and F | On same side of lens | Virtual, erect | Enlarged |
Image Formation by Concave Lens
| Object Position | Image Position | Nature | Size |
|---|
| At infinity | At focus on same side | Virtual, erect | Highly diminished |
| Anywhere in front | Between focus and lens | Virtual, erect | Diminished |
Quick Comparison Table
| Defect | Problem | Cause | Image Position | Lens Used |
|---|
| Myopia | Distant not clear | Long eyeball | Before retina | Concave |
| Hypermetropia | Near not clear | Short eyeball | Behind retina | Convex |
| Presbyopia | Near vision weak | Weak ciliary muscles | — | Convex/Bifocal |
| Astigmatism | Blurred all distances | Irregular cornea | Uneven | Cylindrical |
• The centres of curvature of a thin lens lie on the optical axis where its curved surfaces would form complete spheres.
• In a thin lens, the centres of curvature are positioned symmetrically and equidistant from the optical centre.
• The focal length of a concave mirror depends only on its curvature and is independent of the surrounding medium.
• A negative magnification in spherical mirrors indicates that the image formed is inverted.
• In mirrors, an inverted image is always real.
• A real image is formed when reflected rays actually converge at a point.
• The Tyndall effect is the scattering of light by small particles present in a medium.
• The colour of scattered light depends on the size of the scattering particles.
• Smaller particles scatter shorter wavelengths (blue and violet) more effectively.
• Larger particles scatter longer wavelengths (red and orange) more effectively.
• Isaac Newton first obtained the spectrum of sunlight using a glass prism in 1666.
• Newton conducted his prism experiments at Woolsthorpe, England, during the Great Plague.
• The principal focus of a spherical mirror is fixed at half the radius of curvature (f = R/2).
• The focal length of a mirror does not depend on the size of the mirror.
• The incident ray, refracted ray, and normal at the point of incidence lie in the same plane.
• According to Snell’s Law, for a given pair of media and a given colour of light, the ratio sin i / sin r is constant.