Samacheer Kalvi 10th Science Chapter 22 Short Answer Questions — Visual Communication with Answers
Short answer questions from Samacheer Kalvi Class 10 Science Chapter 22 Visual Communication with detailed answers for 2 and 3 mark questions.
Updated 25 May 20267 min read
Chapter 22 — Visual Communication: Short Answer Questions
1. Describe the structure of the human eye with the function of each part.
Answer
The human eye is a spherical organ of about 2.5 cm diameter, protected by the bony socket (orbit) and eyelids.
Part
Structure
Function
Cornea
Transparent, curved front surface
Primary refraction — provides ~70% of focusing power
Sclera
White, tough outer coat
Protects eyeball; maintains shape
Iris
Coloured muscular diaphragm
Controls pupil size — regulates light entering the eye
Pupil
Opening at centre of iris
Allows light to enter
Lens
Biconvex, transparent, elastic
Fine-focus adjustment (accommodation); can change shape
Aqueous humour
Watery fluid between cornea and lens
Maintains shape of front of eye; nourishes cornea and lens
Vitreous humour
Jelly-like fluid behind lens
Maintains spherical shape of eyeball
Retina
Inner layer of photoreceptors
Detects light; converts to nerve signals
Fovea (yellow spot)
Central region of retina
Highest concentration of cones — sharpest vision
Blind spot (optic disc)
Where optic nerve exits
No photoreceptors — no image detected here
Optic nerve
Bundle of nerve fibres
Transmits signals from retina to the visual cortex of brain
2. Distinguish between rods and cones in the human retina.
Answer
Feature
Rods
Cones
Number
~120 million
~6–7 million
Location
Spread across entire retina except fovea
Concentrated in the fovea (centre of retina)
Sensitive to
Dim/low light (night vision)
Bright light; different wavelengths for colour
Colour detection
Cannot detect colour (monochromatic)
Detect colour — 3 types (red, green, blue wavelengths)
Visual acuity
Low
High (sharp, detailed vision)
Photopigment
Rhodopsin (visual purple)
Photopsins (3 types: red, green, blue)
Function
Night vision; motion detection
Daytime vision; colour vision; fine detail
Note: In very dim light, only rods function — that's why we can't see colours well in the dark, and why objects look clearer slightly off-centre (more rods there).
3. What are the defects of vision? How are they corrected?
1. Myopia (Near-sightedness):
Answer
Problem: Cannot see distant objects clearly; image of distant objects forms in front of retina
Causes: Eyeball too long (antero-posterior diameter increased), or eye lens too curved
Correction:Concave (diverging) lens — diverges light rays before they enter the eye so they focus exactly on retina
2. Hypermetropia (Far-sightedness):
Answer
Problem: Cannot see nearby objects clearly; image of near objects forms behind retina
Causes: Eyeball too short, or eye lens too flat, or ciliary muscles too weak
Correction:Convex (converging) lens — converges light rays so they focus on retina
3. Presbyopia:
Answer
Problem: Age-related (usually after 40) loss of ability to focus on nearby objects
Correction:Bifocal lenses — upper part is concave (for distance), lower part is convex (for near vision)
4. Astigmatism:
Answer
Problem: Blurred or distorted vision at all distances; horizontal and vertical lines cannot be in focus simultaneously
Cause: Uneven curvature of the cornea or lens (not perfectly spherical)
Correction:Cylindrical lenses — designed to correct uneven curvature
4. Explain the structure and working of a simple camera. Compare it with the human eye.
Answer
Structure of a simple camera:
Part
Function
Convex lens
Focuses light from objects onto film/sensor
Aperture (diaphragm)
Opening that controls the amount of light entering
Shutter
Mechanical device that controls how long light hits the film
Film or digital sensor (CCD/CMOS)
Records the image — sensitive to light
Light-proof box
Prevents stray light from entering
Working1. Light from the object enters through the lens 2. Convex lens converges light to form a real, inverted image on the film/sensor 3. Aperture is adjusted to control brightness 4. Shutter speed is adjusted to control exposure time 5. Film/sensor records the image
Comparison: Camera vs Human Eye
Feature
Camera
Human Eye
Focusing
Moving the lens closer/farther from film
Changing shape of the lens (accommodation by ciliary muscles)
Light control
Aperture diaphragm
Iris controls pupil size
Image recording
Film or digital sensor
Retina (rods and cones)
Image type
Single static image
Continuous stream of images
Processing
Computer/darkroom
Brain (visual cortex)
Self-cleaning
No
Yes (tears and blinking)
5. What is persistence of vision? How is it applied in cinema and animation?
Answer
Persistence of vision is the phenomenon where the retina retains the impression of an image for about 1/16th of a second (0.0625 seconds) after the object has been removed from view.
Cause: The photoreceptors (rods and cones) continue to send nerve signals to the brain for a brief time after the stimulus is gone. The brain perceives this lingering image as still present.
Applications:
1. Cinema (Motion Pictures):
Answer
Still photographs (frames) are projected at 24 frames per second (fps)
Due to persistence of vision, each frame appears to blend with the next
The brain perceives this sequence as continuous motion
This is why movies appear as smooth motion rather than flickering individual photographs
2. Television:
Answer
Images are refreshed at 25 fps (PAL system) or 30 fps (NTSC system)
Same principle applies
3. Animation:
Answer
Traditional animation draws slightly different images on each frame
At 24+ fps, the brain combines them as smooth movement
4. Historical devices:
Answer
Phenakistoscope (1832) and Zoetrope — early animation devices based on this principle
Thaumatrope — spinning disc with images on both sides that merge
Threshold: Below ~16 fps, the brain perceives flickering rather than continuous motion (the "flicker fusion frequency").
6. What is film photography? Explain the chemistry behind it.
Answer
Film photography uses light-sensitive chemical coatings on film to record images.
Photographic film composition:
Plastic base coated with gelatin emulsion containing silver halide crystals (mainly silver bromide AgBr, also AgCl and AgI)
Formation of a latent image:
When light strikes silver halide crystals, a photochemical reaction occurs:
This makes the image permanent and stable in normal light
Printing:
Light is shone through the negative onto photographic paper
Same chemistry produces a positive print
Digital photography replaced this process using CCD/CMOS sensors that convert light directly to electrical signals.
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Frequently Asked Questions
Camera vs human eye: Lens (camera) = cornea + eye lens (eye) — both focus light. Aperture/diaphragm (camera) = iris/pupil (eye) — both control amount of light entering. Film/digital sensor (camera) = retina (eye) — both record the image. Both form real, inverted images. The camera shutter controls exposure time; the eye relies on continuous processing. The camera records a single image; the retina continuously sends signals to the brain.
