Human Eye and Visual Defects
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Questions and Answers

What is the name of the transparent front projected part of the eyeball?

Cornea

The ______ controls the level of light entering the eye.

iris

What is the function of the choroid?

It helps to keep the eye dark by absorbing diffused light falling on it and prevents internal reflections within the eye.

What is the function of the ciliary muscles?

<p>They control the focal length of the eye lens.</p> Signup and view all the answers

What is the function of the optic nerve?

<p>It carries electrical signals from the retina to the brain.</p> Signup and view all the answers

What are the two types of vision cells found in the retina?

<p>Rods and cones</p> Signup and view all the answers

What is the name of the point where the optic nerve enters the eyeball?

<p>Blind spot</p> Signup and view all the answers

What is the name of the slightly raised spot with a minute depression in its peak located at the center of the retina?

<p>Yellow spot</p> Signup and view all the answers

What is the process of changing the focal length of the eye lens called?

<p>Accommodation</p> Signup and view all the answers

What is the nearest point to which the eye can see clearly called?

<p>Near point</p> Signup and view all the answers

What is the farthest point that an eye can see clearly called?

<p>Far point</p> Signup and view all the answers

Why are bees able to see ultraviolet light, but humans can't?

<p>Bees have cone cells in their retina that are sensitive to ultraviolet light, while humans do not.</p> Signup and view all the answers

The human eye can see clearly objects situated anywhere from 25 cm to infinite distances.

<p>True (A)</p> Signup and view all the answers

Define the power of accommodation of the human eye.

<p>Power of accommodation is the ability of the eye to adjust the focal length of the eye lens to see clearly both nearby and distant objects.</p> Signup and view all the answers

What is the maximum power of accommodation for a person with normal vision?

<p>The maximum power of accommodation for a person with normal vision is about 4 dioptre.</p> Signup and view all the answers

What is the name of the defect of vision that makes it difficult for people to see distant objects clearly?

<p>Myopia or near-sightedness</p> Signup and view all the answers

What type of lens should be used to correct myopia?

<p>Concave lens</p> Signup and view all the answers

What is the name of the defect of vision that makes it difficult for people to see nearby objects clearly?

<p>Hypermetropia or far-sightedness</p> Signup and view all the answers

What type of lens should be used to correct hypermetropia?

<p>Convex lens</p> Signup and view all the answers

What is the name of the defect of vision that often develops with age, making it difficult to focus on nearby objects?

<p>Presbyopia</p> Signup and view all the answers

What is the name of the defect of vision that makes it difficult to see both horizontal and vertical lines simultaneously?

<p>Astigmatism</p> Signup and view all the answers

What type of lens should be used to correct astigmatism?

<p>Cylindrical lens</p> Signup and view all the answers

What is meant by persistence of vision?

<p>Persistence of vision is the ability of the eye to retain an image for about 1/16th of a second even after the object is removed.</p> Signup and view all the answers

What is the name of the phenomenon that explains why a beam of light becomes visible as it passes through dust particles in a room?

<p>Tyndall effect</p> Signup and view all the answers

What is the name of the colored band of light produced when white light splits into its constituent colors?

<p>Spectrum</p> Signup and view all the answers

What is the name of the natural phenomenon that is responsible for the formation of a rainbow?

<p>Dispersion of light</p> Signup and view all the answers

What is the name of the process by which light bends as it passes from one medium to another, such as air to water?

<p>Refraction</p> Signup and view all the answers

Stars appear to twinkle due to the refraction of starlight passing through the earth's atmosphere.

<p>True (A)</p> Signup and view all the answers

The sun appears oval at sunset due to the refraction of light passing through the earth's atmosphere.

<p>True (A)</p> Signup and view all the answers

What is the cause of the blue color of the sky?

<p>The scattering of blue light by the particles in the atmosphere.</p> Signup and view all the answers

Why do the clouds appear white?

<p>The scattering of all colors of light by the large dust particles and water droplets contained in the clouds.</p> Signup and view all the answers

Why are danger signals often red in color?

<p>Red light is scattered the least by fog and smoke, making red signals more visible in foggy or smoky weather than other colors.</p> Signup and view all the answers

Why do car headlights use yellow light in foggy weather?

<p>Yellow light has a longer wavelength than blue light and is scattered less by fog. This makes yellow headlights easier to see and travel farther in foggy conditions.</p> Signup and view all the answers

What is the main reason the sky often appears greyish over cities with industrial units?

<p>The presence of small dust particles and smoke from industrial units scatter short wavelengths of light, such as red, orange, and yellow, more effectively than other colors, resulting in a greyish sky.</p> Signup and view all the answers

Planets do not twinkle because they are much farther away from the Earth than stars.

<p>False (B)</p> Signup and view all the answers

What are the reasons why the sun appears oval at sunrise and sunset but circular at noon?

<p>The sun appears oval at sunrise and sunset because the rays of light from the upper and lower edges of the sun bend at different angles as they pass through the Earth's atmosphere. The sun is overhead at noon, and so its rays enter the atmosphere at a nearly perpendicular angle, resulting in minimal bending and a more circular appearance.</p> Signup and view all the answers

Study Notes

Human Eye and Colourful World

  • The human eye is a complex natural optical instrument
  • Its diameter is approximately 2.3 cm
  • Essential parts of the eye:
    • Sclerotic: Outermost layer, tough, white, protects the eye
    • Cornea: Transparent front part, refracts light
    • Choroid: Grey-black layer, absorbs light, prevents internal reflections
    • Iris: Dark muscular diaphragm, controls light
    • Pupil: Central aperture in the iris, adjusts size
    • Crystalline lens: Adjusts focal length for focusing
    • Ciliary muscles: Controls focal length of the lens
    • Optic nerve: Carries electrical signals to the brain

Accommodation of the Eye

  • A normal eye can focus objects at varying distances
  • The eye lens changes its focal length through ciliary muscles' action
  • To see far objects, ciliary muscles relax, increasing lens thickness
  • To see near objects, ciliary muscles contract, decreasing lens focal length

Defects of Vision

  • Myopia (Nearsightedness):
    • Person can see nearby objects but not distant ones
    • Images are formed in front of the retina
    • Corrected with concave lenses
  • Hypermetropia (Farsightedness):
    • Person can see distant objects but not nearby ones
    • Images are formed behind the retina
    • Corrected with convex lenses
  • Presbyopia (Old Age Hypermetropia):
    • Gradual weakening of ciliary muscles and lens flexibility
    • Results in decreased ability to accommodate near objects
    • Corrected with bifocal lenses (concave for distance, convex for near)
  • Astigmatism:
    • Irregular curvature of the cornea or lens
    • Images are not properly focused
    • Corrected with cylindrical lenses

Persistence of Vision

  • The image persists on the retina for a fraction of a second
  • It gives a sense of continuous motion in movies and animations

Atmospheric Refraction

  • Light bends as it passes through layers of different densities
  • Twinkling of stars is due to continuous changes in atmospheric density causing light to bend
  • Sun appears oval at sunrise/sunset due to light bending, whereas higher in the sky light follows relatively straight paths

Scattering of Light

  • Scattering occurs when light interacts with particles in the atmosphere
  • Rayleigh scattering: Scattering of shorter wavelengths more than longer wavelengths
  • Tyndall effect: Scattering of light by colloidal particles (e.g., dust, smoke)

Dispersion of White Light

  • White light is a mixture of all colors
  • White light is separated into its constituent colors when it passes through a prism (e.g., a water droplet)
  • Colors are dispersed based on their wavelengths, with violet having the shortest and red the longest

The Rainbow

  • A dispersion of sunlight into a spectrum of colors
  • Occurs when sunlight is refracted, reflected, and refracted again within water droplets
  • The order of colors in a rainbow is red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)

Colour of the Sky

  • The sky appears blue due to the scattering of blue light by air molecules (Rayleigh scattering)
  • The color of the sun at sunset/sunrise appears red/orange due to longer wavelengths' less scattering

Advanced Sunrise and Delayed Sunset

  • Apparent positions of the sun differ from the actual sunrise/sunset positions
  • These discrepancies are caused by atmospheric refraction

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Human Eye and Colourful World PDF

Description

Explore the fascinating intricacies of the human eye, from its essential parts to how it accommodates different distances. This quiz also addresses common vision defects such as myopia. Test your understanding of the eye's functions and mechanisms.

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