Class 10 Science: Human Eye and the Colorful World

Early Sunrise and Delayed Sunset

Key Points:

• Early Sunrise: The Sun begins to appear a bit before the actual sunrise.
• Delayed Sunset: The Sun remains visible for a little while even after the actual sunset.

Cause:

1. Earth and Atmosphere:
   • The effect of the Earth's surface and atmosphere.
   • The position of the Sun above or below the horizon.
2. Refraction of Light:
   • When the Sun's rays enter the atmosphere, they pass from a rarer medium to a denser medium.
   • Bending of rays towards the normal.
   • Our eyes perceive the bent rays above the horizon, making the Sun appear before and after its actual position.

Time Duration:

• Due to this phenomenon, the length of the day appears to be about 4 minutes longer.

How to Write Answers in Exams:

1. Answer Format:
   • Give a clear answer to the question.
   • Draw appropriate diagrams.
   • Keep diagrams neat and clear.
   • Write answers in the language of the textbook.
2. Diagram:
   • Show the Sun, Earth, atmosphere, and horizon.
   • Depict the refraction of rays going from rarer to denser medium.

Conclusion:

• Understand and memorize the entire concept.
• Comprehend properly and write instead of rote learning.
• See you in the next class.