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Materials required: Light source, 2 pins, 2 glass prisms, marker, paper.

Procedure:

-Take a piece of paper, put 2 glass prisms in such a way that the second one is inverted with respect to the first one and trace the outline of the glass prisms.

-Direct the ray of light towards one of the prisms. Trace the light ray and the spectrum between the prisms and put two pins, one in the incident ray and another in emergent ray after the second prism.

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1.      State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms, show that white light is made of seven colours? Draw a ray diagram to show the path of a narrow beam of white light, through

a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination.

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This phenomenon occurs exclusively in triangular prisms because the sides of the glass prisms are not parallel to each other. But in a glass slab, because of its rectangular shape, the sides are parallel to each other. Therefore, dispersion of light could not occur in a glass slab.

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1.      Describe an activity to show that the colours of white light split by a glass prism can be recombined to get white light by another identical glass prism. Also draw ray diagram to show the recombination of the spectrum of white light.

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A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why it is so.

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The two causes leading to myopia are:

-Increase in curvature of eye-lens.

-Increase in length of eye-ball.

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Increase in curvature of eyelens.

Elongation of eyelens

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State the two causes of myopia

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Presbyopia is defined as an old-age defect where a person cannot see nearby objects clearly. This is caused due to

-The weakening of the ciliary muscles due to age.

-The weakening of the eye-lens.

Their near point will be greater than 25cm.

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What is Presbyopia? Write two causes of this defect.

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The sun can be seen about 2 minutes before the actual sunlight due to atmospheric refraction. The rays of light travelling from the sun undergoes continual refraction upon entering the atmosphere. Therefore, the sun's apparent position to the observer is higher than the actual position of the sun.

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the refraction from earth's atmosphere and the distance between the earth and the sun

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Refarction of the sunlight towards the horizon causes this

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Why the sun can be seen about two minutes before actual sunrise.

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Colour of the clear sky during noon appears blue. This is because of dispersion of sunlight into various colours. Here, our atmosphere acts as a giant refractive medium. Once the sun appears directly above the sky, the atmosphere disperses light. Here, blue is visible beacuse the atmosphere can scatter colours of shorter wavelength. Since blue has a shorter wavelength, blue gets scattered the most. Also, the particles of blue light is similar in size to those of the atmosphere. Therefore the clear sky appears blue.

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The blue light is scattered more than the red light because blue color has the smallest wavelength almost equal to the size of the particles present in our atmosphere. So, it is scattered the most, causing the sky to be blue

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It is because blue has a shorter wavelength

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The blue light is scatteredmore than any other colour

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A.      Give reasons for the following :

i.        Colour of the clear sky is blue.

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Hypermetropia or far-sightedness is defined as an eye defect where a person can see far-off objects clearly but cannot see nearby objects clearly. This is caused due to

-decrease in the curvature of eyelens.

-decrease in height of eyeball.

In this, the image is formed behind the retina.

The suitable lens used for this is convex lens.

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Dispersion is the scattering of white light into its constituent colors (VIBGYOR)

Rainbows are formed when the tiny water droplets in the air act as prisms and scatter white light into its constituent colors. This phenomena usually occurs after rain.

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Hypermetropia or long-sightedness is when the eye can't see near objects but can see far objects. This can because of the decrease of the curvature. It can be fixed by wearing convex lens

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What is hypermetropia? Draw ray diagrams to show the image formation of an object by :

i.        Hypermetropic eye

ii.      Correction made with a suitable lens for hypermetropic eye.

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Dispersion of light is defined as the separation of white light into 7 colours such as Violet, Indigo, Blue, Green, Yellow, Orange and Red upon passing the white light through a sphere. This same phenomena explains the mysterious formation of rainbows. Rainbows occur after a light shower. Upon passing through a raindrop, the sunlight disperses into the 7 said colours. These 7 colours reach our eyes as a bow-like formation.

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Splitting of light into 7 colors which are Violet, Indigo, Yellow, orange, green, blue, Red

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When white light goes through a prism, the light split into a band of colours called the spectrum.

The white light disperses when light passes through the water droplets forming a rainbow.

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Dispersion is when white light is split into 7 colors called VIBGYOR.

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dispersion- splitting of white light into its constituent 7 colours

Violet,Indigo,Blue,Green,Yellow,Orange,Red

Rainbow is formed due to refraction in raindrops which splits the white light of sun into its constituent colours forming the rainbow it is formed in the opposite direction to the sun

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dispersion of white light means to split the white light into it's constituent colours called the spectrum.

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Ciliary Musceles

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Ciliary muscles

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What is meant by dispersion of white light? Describe the formation of rainbow in the sky.

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Ciliary Muscles

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ciliary muscles

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Ciliary muscles

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Ciliary muscles

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ciliary muscles

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Eye Lens

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1.      Name the part of our eyes that helps us to focus near and distant objects in quick succession.