Science Class 10 - Human Eye-And-Colourful-World Notes

Human Eye and Colourful World

Welcome to the chapter on Human Eye and Colourful World for Class 10. In this chapter, you will learn about the structure and function of the human eye, how we see objects, defects of vision and their correction, and the fascinating phenomena of the colourful world around us. By the end of this chapter, you will understand how the eye works and why the sky is blue and sunsets are red!

Key Concepts

• Human Eye: The sense organ that helps us see the world.
• Retina: The screen at the back of the eye where images are formed.
• Lens: A transparent structure that focuses light on the retina.
• Accommodation: The ability of the eye lens to adjust its focal length to see near and distant objects clearly.
• Defects of Vision: Problems like myopia (short-sightedness), hypermetropia (long-sightedness), and presbyopia.
• Dispersion: Splitting of white light into its seven colours.
• Atmospheric Refraction: Bending of light as it passes through the atmosphere, causing phenomena like twinkling of stars.

Structure and Function of the Human Eye

• Cornea: The transparent front part that lets light enter the eye.
• Iris: The coloured part that controls the size of the pupil.
• Pupil: The opening that lets light into the eye.
• Lens: Focuses light onto the retina.
• Retina: Contains cells that sense light and send signals to the brain.
• Optic Nerve: Carries signals from the eye to the brain.

The eye forms an inverted image on the retina, which the brain interprets as upright.

Power of Accommodation

The eye lens changes its shape to focus on objects at different distances. This is called accommodation. The least distance at which the eye can see clearly is called the near point (about 25 cm for a normal eye).

Defects of Vision and Their Correction

• Myopia (Short-sightedness): Can see near objects clearly but not distant objects. Corrected by using concave lenses.
• Hypermetropia (Long-sightedness): Can see distant objects clearly but not near objects. Corrected by using convex lenses.
• Presbyopia: Old-age defect where the eye loses its power of accommodation. Corrected by using bifocal lenses.

Colourful World

• Dispersion of Light: When white light passes through a prism, it splits into seven colours (VIBGYOR).
• Rainbow: Formed by dispersion, refraction, and reflection of sunlight in water droplets.
• Atmospheric Refraction: Causes twinkling of stars, advanced sunrise, and delayed sunset.
• Scattering of Light: Causes the sky to appear blue and the sun to look red at sunrise and sunset.

Practice Questions

1. Name the part of the eye where the image is formed.
2. What is the function of the iris?
3. How is myopia corrected?
4. Why does the sky appear blue?
5. What is dispersion of light?

Challenge Yourself

• Draw and label the parts of the human eye.
• Explain why the sun appears red at sunrise and sunset.
• Describe how a rainbow is formed in the sky.

Did You Know?

• The human eye can distinguish about 10 million different colours!
• The blinking of the eye helps keep it clean and moist.

Glossary

• Retina: The light-sensitive layer at the back of the eye.
• Accommodation: The ability of the eye lens to focus on near and far objects.
• Dispersion: Splitting of white light into its different colours.
• Scattering: Spreading of light in different directions by particles in the atmosphere.

Answers to Practice Questions

1. Retina
2. It controls the size of the pupil and the amount of light entering the eye.
3. By using concave lenses.
4. Because of the scattering of blue light by the atmosphere.
5. Splitting of white light into seven colours when it passes through a prism.

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The human eye is a wonderful organ. Explore the colourful world around you and discover the science behind what you see!