Lenses
A lens is a piece of transparent material with curved surface. There are two types of lenses : convex lens and concave lens.
All lenses are thinner at the edges and thicker at the centre.
| | Case 1 | Case 2 |
| Object distance from lens | Long | Short |
| Image obtained: | Inverted | Upright |
| On the opposite side of lens as the object | On the same side of lens as the object | |
| Diminished | Magnified | |
| Real | Virtual |
Kinds of images:
1) virtual image : it cannot be captured on the screen because no actual light rays meet at an image position.
2) real image: light rays meet at an image point and thus the image can be captured on the screen.
Terms used in ray diagram for lenses:
Optical centre - point at centre of lens
Principal axis - line passing symmetrically through optical centre of lens
Principal focus - point where all rays close to and parallel to the principal axis converge after refraction by lens
Focal length - distance between optical centre and focal point
Focal plane - plane passing through focal length and perpendicular to principal axis
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