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How Nature Works in Harmony - How Do We Experience and Interpret Nature?

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Nature is experienced primarily through our senses, with sight being one of the most vital. We see objects because of the reflection of light from their surfaces into our eyes.

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The Law of Reflection states that the angle of incidence ∠i\angle i is always equal to the angle of reflection ∠r\angle r. Additionally, the incident ray, the reflected ray, and the normal at the point of incidence all lie in the same plane.

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Regular reflection occurs on smooth surfaces (like mirrors), while diffused or irregular reflection occurs on rough surfaces, allowing us to see non-shiny objects from different angles.

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The Human Eye interprets nature by focusing light through the lens onto the retina. The retina contains two types of light-sensitive cells: Cones (sensitive to bright light and color) and Rods (sensitive to dim light).

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Dispersion of light is the phenomenon where white light splits into its seven constituent colors (VIBGYOR) when passing through a medium like a prism or water droplets, creating a rainbow.

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Persistence of Vision: The impression of an image stays on the retina for about 116\frac{1}{16} of a second. If images are flashed faster than this, they appear as a continuous moving picture.

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The Braille system is a tactile code that enables visually challenged people to read and write, interpreting nature and information through the sense of touch.

📐Formulae

∠i=∠r\angle i = \angle r

n=(360∘θ)−1n = \left( \frac{360^{\circ}}{\theta} \right) - 1

Persistence of Vision=116 second\text{Persistence of Vision} = \frac{1}{16} \text{ second}

💡Examples

Problem 1:

If two plane mirrors are placed at an angle of 90∘90^{\circ} to each other, how many images of an object placed between them will be formed?

Solution:

n=360∘90∘−1=4−1=3n = \frac{360^{\circ}}{90^{\circ}} - 1 = 4 - 1 = 3

Explanation:

Using the formula for multiple reflections where θ=90∘\theta = 90^{\circ}, we divide 360360 by the angle and subtract 11 to find the number of images seen.

Problem 2:

An incident ray makes an angle of 35∘35^{\circ} with the surface of a plane mirror. Calculate the angle of reflection.

Solution:

First, find the angle of incidence ∠i\angle i by subtracting the surface angle from the normal (90∘90^{\circ}): 90−3555\begin{array}{r} 90 \\ - 35 \\ \hline 55 \end{array} Therefore, ∠i=55∘\angle i = 55^{\circ}. According to the Law of Reflection, ∠r=∠i=55∘\angle r = \angle i = 55^{\circ}.

Explanation:

The angle of incidence is measured between the normal and the incident ray, not the mirror surface. Once ∠i\angle i is found, it is equal to the angle of reflection ∠r\angle r.