Lesson 9 of 11
The big picture
Show on a big screenOne lens, two fixes, an older eye, one prism, one sky.
| Idea | The rule |
|---|---|
| The eye is a lens | Light enters through the cornea. The lens forms a real, upside-down image on the retina. The optic nerve carries the signal to the brain. |
| Focusing near and far | The eye lens changes shape to focus. Ciliary muscles relax for far objects and contract for near ones. The nearest sharp distance is the near point, about 25 cm. |
| When far things blur | In myopia, distant objects focus in front of the retina. A concave lens fixes it. The lens must put far objects at the far point. |
| When near things blur | In hypermetropia, near objects focus behind the retina. A convex lens fixes it. The lens puts a 25 cm object's image at the near point. |
| The eye with age | With age, the near point moves farther away. A convex lens helps with reading. A bifocal lens has a concave top, for far. Its bottom is convex, for near. |
| Light comes apart | A prism splits white light into seven colours. Violet bends the most and red bends the least. This splitting is called dispersion. |
| Why the sky is blue | Air scatters short waves like blue more than long waves like red. The scattered blue light makes the sky look blue. With no air, the sky would look dark. |
| The Sun at the edge of the day | Near the horizon, sunlight crosses much more air. More blue scatters out. The red light that is left makes the Sun look red. |
Now open Chapter 10 in your NCERT book. It is The Human Eye and the Colourful World. You have worked out its main numbers yourself.