The eye is a lens instrument
Show on a big screenThe eye is like a camera. It has a lens and a light-sensitive screen. Light-sensitive means it reacts to light. The screen is where the picture forms. Rays are thin beams of light.
- Light enters the eye from the left.
- The iris is a ring of muscle. It sets the size of the pupil, the opening for light.
- The eye lens bends the rays. Muscles hold it in place.
- The rays cross on the retina, the screen at the back. That is the image.
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Read each job. Tap the part that does it.
The rule
The eyeball is about 2.3 cm across. The cornea is a clear bulge at the front. The cornea does most of the bending. The lens then makes a small final change to the focus. To focus is to bring rays to one point.
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.
A real image is one that forms where rays meet.
| Part | Job |
|---|---|
| Iris | A ring of muscle that sets the size of the pupil |
| Pupil | The opening that lets light in |
| Ciliary muscles | Change the shape of the lens |
| Retina | The light-sensitive screen where the image forms |
| Optic nerve | Carries signals from the retina to the brain |
Watch out!
The image on the retina is upside down. Nothing is wrong. The brain reads the signals, so you see things as they are.
Try the lab to finish this lesson.