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Light - Care of Eyes and the Braille System

Grade 8CBSE

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

🔑Concepts

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Reading in very little or too much light is bad for the eyes; insufficient light causes eye strain and headaches, while too much light can injure the retina.

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Do not look at the sun or a powerful light source directly to avoid damage from intense radiation.

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The normal distance at which one can read clearly is about 25 cm25\text{ cm}. Reading too close or too far can lead to vision issues.

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Vitamin A deficiency leads to Night Blindness; therefore, one should include Vitamin A-rich foods like raw carrots, broccoli, green vegetables, and cod liver oil in the diet.

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Visually impaired persons can read and write using the Braille system, which is a non-optical aid.

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The Braille system was developed by Louis Braille in 18211821. It consists of 6363 dot patterns or characters.

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In the Braille system, each character represents a letter, a combination of letters, a common word, or a grammatical sign.

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Dots in a Braille cell are arranged in two vertical rows of three dots each, allowing for tactile recognition.

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Optical aids for the visually impaired include bifocal lenses, contact lenses, tinted lenses, magnifiers, and telescopic aids.

📐Formulae

∠i=∠r\angle i = \angle r

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

Minimum Distance for Distinct Vision≈25 cm\text{Minimum Distance for Distinct Vision} \approx 25\text{ cm}

💡Examples

Problem 1:

Calculate the number of images formed if two plane mirrors are placed at an angle of 90∘90^{\circ} to each other.

Solution:

Using the formula n=(360∘θ)−1n = \left( \frac{360^{\circ}}{\theta} \right) - 1, we substitute θ=90∘\theta = 90^{\circ}: n=(360∘90∘)−1=4−1=3n = \left( \frac{360^{\circ}}{90^{\circ}} \right) - 1 = 4 - 1 = 3.

Explanation:

When two mirrors are kept at an angle, multiple reflections occur. The number of images nn depends on the angle θ\theta between the mirrors.

Problem 2:

A student is unable to see the blackboard clearly while sitting at a distance. What nutrient might be lacking in their diet if they also struggle to see in dim light?

Solution:

The student is likely suffering from Night Blindness caused by a deficiency of Vitamin A.

Explanation:

Vitamin A is essential for the production of rhodopsin in the rod cells of the retina, which helps in seeing under low light conditions. Sources include C20H30OC_{20}H_{30}O (Retinol) found in carrots and milk.

Problem 3:

How many dot patterns are used in the Braille system for visually challenged people?

Solution:

There are 6363 dot patterns or characters available in the Braille system.

Explanation:

The system uses cells of 2×32 \times 3 dots where patterns are embossed to be felt by touch. Each pattern represents a specific linguistic or mathematical symbol.