Chapter 22 — Visual Communication: Multiple Choice Questions
1. The part of the human eye that controls the amount of light entering is the ______.
- Bright light → iris constricts → pupil becomes small → less light
- Dim light → iris dilates → pupil becomes large → more light
The cornea refracts light; the lens focuses it; the retina detects it.
2. The image formed on the retina of the human eye is ______.
3. The photoreceptors in the retina sensitive to colour are called ______.
- Rods (~120 million): Sensitive to dim light (night vision); cannot distinguish colours
- Cones (~6–7 million): Require bright light; responsible for colour vision (3 types: red, green, blue wavelengths); concentrated in the fovea (point of sharpest vision)
4. The minimum distance at which the human eye can see objects clearly without strain is ______.
5. Persistence of vision is approximately ______.
- Cinema (movies shown at 24 fps)
- Television (25 or 30 fps)
- Animation
- Phenakistoscope and other early animation devices
6. The defect of vision in which the person cannot see nearby objects clearly is called ______.
- Hypermetropia (far-sightedness): Cannot see nearby objects clearly; image forms behind retina. Corrected by convex lens.
- Myopia (near-sightedness): Cannot see distant objects; image forms in front of retina. Corrected by concave lens.
- Presbyopia: Age-related loss of near vision (eye lens loses flexibility). Bifocal lenses.
- Astigmatism: Uneven curvature; cylindrical lenses.
7. A camera records images on ______.
- Lens → focuses light (like eye lens)
- Aperture → controls light (like iris/pupil)
- Shutter → controls exposure time
- Film/sensor → records image (like retina)
Digital cameras use CCD or CMOS sensors to record images electronically, replacing photographic film.
8. The principle behind photography using light-sensitive silver salts is used in ______.
9. The blind spot in the eye is located where ______.
10. Which lens is used in a simple camera?
Quick Revision — Human Eye
| Part | Function |
|---|---|
| Cornea | Primary refraction (responsible for 2/3 of eye's focusing power) |
| Aqueous humour | Maintains eye pressure, nourishes cornea and lens |
| Iris | Controls pupil size — regulates light entry |
| Pupil | Opening through which light enters |
| Lens | Fine-focus adjustment (accommodation) |
| Vitreous humour | Fills eyeball, maintains shape |
| Retina | Detects light; has rods (dim light) and cones (colour) |
| Fovea | Highest concentration of cones; sharpest vision |
| Blind spot | No photoreceptors; where optic nerve exits |
| Optic nerve | Transmits signals from retina to brain |
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Frequently Asked Questions
Camera: Lens focuses light onto film/sensor; aperture (like iris) controls light; shutter speed controls exposure time. Human eye: Cornea + eye lens focus light onto retina; iris controls light entering; retina has photoreceptors (rods for dim light, cones for colour). Both form inverted, real images.