The Human Eye Quiz

The Human Eye

• The human eye is similar to a camera, forming an inverted, real image on the light-sensitive retina.
• The cornea is a transparent membrane where most light refraction occurs.
• The iris controls the size of the pupil.
• The pupil is a black opening that regulates light entering the eye.
• The crystalline lens focuses light onto the retina.
• Ciliary muscles adjust the lens curvature to focus on objects at different positions, enabling clear vision.
• Light-sensitive cells in the retina convert light into electrical signals, which are sent to the brain via the optic nerve for interpretation.
• The iris adjusts the pupil size in response to light intensity.
  • In bright light, the iris contracts the pupil, reducing light entering the eye.
  • In dim light, the iris expands the pupil, increasing light entering the eye.
• Persistence of vision refers to the lingering sensation of an object after it is removed from view. This lasts approximately 1/16th of a second.

Eye Defects and Corrections

• Hypermetropia (Farsightedness): Inability to see nearby objects clearly. Causes:

  • Eye lens is too thin.
  • Eyeball is too small.

• Correction: Using a convex lens with suitable power.

• Myopia (Nearsightedness): Inability to see distant objects clearly, occurs when:

  • Eye lens is too thick.
  • Eyeball is too long.

• Correction: Using a concave lens with suitable power.

• Presbyopia: Gradual weakening of ciliary muscles and decreasing lens flexibility with age. This leads to nearsightedness.

• Correction: Using bifocal lenses, which combine concave and convex lenses to correct for both nearsightedness and farsightedness.

Refraction of Light

• A prism has two triangular bases and three rectangular surfaces.
• The angle between two adjacent lateral faces is called the angle of the prism.
• Angle of Deviation (D): The angle between the incident ray and emergent ray after light passes through a prism.
• Dispersion of White Light:
  • White light is split into a band of colours (spectrum - VIBGYOR) when it passes through a prism.
  • This happens because different wavelengths of light bend at different angles.
  • Red light bends least, while violet light bends most.
  • Isaac Newton demonstrated that a second prism could recombine the colours of a spectrum back into white light.

Rainbow Formation

• Rainbows are formed when sunlight interacts with tiny water droplets in the atmosphere.
• Water droplets act as prisms, refracting, dispersing, and internally reflecting sunlight.
• The sunlight is refracted and dispersed when entering the water droplet.
• It then undergoes internal reflection within the droplet.
• Finally, it is refracted again when exiting the droplet, producing a spectrum of colors in the sky.
• Rainbows are always formed opposite to the sun's position.

Atmospheric Refraction

• Apparent Star Position: Apparent position of stars is different from their actual position due to atmospheric refraction.

  • Starlight bends as it enters the Earth's atmosphere, making stars appear slightly higher than their actual position.

• Twinkling of Stars: The twinkling of stars is also due to atmospheric refraction.

  • Variations in the Earth's atmosphere cause the amount of light entering the eye to fluctuate, creating the twinkling effect.

• Planets Don't Twinkle: Planets do not twinkle because they are closer to Earth and appear as extended sources of light, with multiple point sources.

• Advance Sunrise and Delayed Sunset: Sun appears about two minutes earlier than actual sunrise and two minutes later than actual sunset due to atmospheric refraction.

  • The light from the sun bends as it enters the Earth's atmosphere, making it appear above the horizon even though the sun is actually below it.

Scattering of Light

• Tyndall Effect: Scattering of light by colloidal particles, making the light beam visible.

• Factors Influencing Scattering:

  • The color of the scattered light depends on the size of the scattering particles.
  • Very fine particles scatter mainly blue light (short wavelengths).
  • Larger particles scatter light of longer wavelengths (red light).
  • Very large particles scatter all wavelengths equally, making the sky appear white.

• Sky Color: The sky appears blue due to Rayleigh scattering.

  • Air molecules and fine particles scatter blue light more effectively than red light, making the daytime sky blue.

• Clouds Appear White: Water droplets in clouds are large enough to scatter all wavelengths of light equally, giving clouds their white appearance.