Science [2 Mark Questions]

Sunrise can be observed two minutes before the sun actually gets above the horizon because of the phenomenon of bending of light as a result of atmospheric refraction. The rays coming from the sun get refracted because of the difference in the density of the atmospheric layers and then reach the observer. Thus, the light coming is perceived as coming from the sun and hence, the sunrise is seen two minutes before it actually rises.

Incident ray, the emergent ray and the angle of deviation is as marked in the diagram below:

When the second identical prism is placed in an inverted position with respect to the first prism recombination of the spectrum from white light again.

A star sometimes appears brighter and some other times fainter because of twinkling effect. Atmospheric refraction gives rise to twinkling effect. Light which is travelling through different layers of the atmosphere bents in different directions making the stars twinkle.

The splitting up of white light into its constituent colours on passing through a refracting medium like a glass prism is called dispersion of light.

Planets, being much closer to the earth are considered as extended source of light. Stars, being distant, are taken as point sized sources of light. The light coming from stars goes on varying due to atmospheric refraction pro-during twinkling effect.

1. X-Violet, Y-Red.
2. Different colors of white light bend through different angles with respect to the incident beam of light due to the difference in speed of light of different wavelengths and Refractive index of glass is different for different colours of light.

Modern periodic table consists of groups and periods. Where number of valence electrons determines the group and number of shells determines the period.

1. Group - 14, Period - 3.
2. Silicon.

Non - metallic/ poor conductor of electricity.

The eye lens being convex in nature converges the light rays incident on it. Hence, it focuses the light falling on it on a thin layer of nerve cells called the retina. Two Ciliary muscles hold the lens within the eye-ball and it relaxes and tightens to change the focal length of the eye lens to get the clear image on the retina.

The ability of the eye lens to adjust its focal length is called the power of accommodation. There should be a contract in ciliary muscles, that will increase the curvature of the eye lens and becomes thicker consequently the focal length of the eye lens will decrease. It will enable us to see near objects clearly.

Following are the advantages of having two eyes instead of one:

1. Having two eyes gives a wider field of view.
2. Having two eyes enables us to judge distances more accurately.

When the sun is setting, the light from it has to travel a greater thickness of the earth's atmosphere and only the longer wavelength red light is able to reach us. Sunset is therefore red in colour.

The band of seven colours formed on a white screen, when a beam of white light is passed through a glass prism is called spectrum of white light. A glass prism is used to produce a spectrum.

1. When we look at our hand, the eye lens is thick. When we look at a nearby object, the eye lens becomes thick or more convex to converge the rays of light from the nearby object (our hand) to form an image on the retina.
2. When we look at a distant tree, the eye lens is thin. When we look at a far-off object, the eye is in a relaxed state. The eye lens becomes thin or less convex because a small converging power of the eye lens is sufficient to focus the parallel light rays from the distant object (the tree) to form an image on the retina.

Ciliary muscles get relaxed and the eye lens becomes thin when the eye is looking at a distant object, and these muscles contract and make the eye-lens thick when the eye is looking at a nearby object. Thus, ciliary muscles help in the normal functioning of the eye by changing thethickness of the eye-lens while focussing.

1. Violet light has the shortest wavelength and is bent the most. Thus violet light travels more slowly through glass than does any other color and red light travels fastest.
2. Red light has maximum wavelength and violet has minimum wavelength. As the frequency and wavelength of a wave are inversely proportional to each other so, red light has minimum frequency and violet light has maximum frequency.

The lens present in human eye is a convex lens. Mostly it forms real and inverted images, but when the object is placed between the focal point and centre of the length then virtual and erect image is formed.

The sun and the surrounding sky appear red at sunrise because at that time most of the blue color present in sunlight has been scattered out and away from our line of sight, leaving behind mainly red color in the direct sunlight beam that reaches our eyes.

1. Cornea: focuses light rays and permits the light to enter the eye.
2. Iris: Controls amount of light entering the eye and controls the size of pupil.
3. Crystalline Lens: Converges light rays onto retina.
4. Cilliary Muscles: Adjusts focal length of eye lens by contraction and relaxation so that sharp image can be obtained on the retina. It helps in accommodation.

Rods are the rod-shaped cells present in the retina of an eye which are sensitive to dim light. Cones are the cone-shaped cells present in the retina of an eye which are sensitive to bright light. Our night vision is relatively poor compared to the night vision of an owl due to the presence of relatively smaller number of rod cells in the retinas of our eye.

If another similar glass prism is placed upside down behind the first prism, then the seven coloured rays from the first prism which are incident on the second prism recombine to form the original white beam.

No rainbow could be observed from the surface of moon by the astronauts because The rainbow is formed only if the atmosphere contain large number of tiny droplets of water suspended in the air. As moon has neither atmosphere nor water therefore no rainbow is formed.

The predators (like lions) have their eyes facing forward at the front of their heads, whereas the animals of prey (like rabbit) usually have eyes at the sides of their head so that they can see their enemies (predators) in a very large area around them and try to escape from them.

It takes some time to see objects in a dim room when we enter the room from bright sunshine outside because it takes some time to the small pupil of our eye to become large so that more light enters our eye and we can see clearly.

When a beam of sunlight enters a dusty room through a window, then its path become visible to us. The tiny dust particles present in the air of room scatter the beam of light all around the room.

When the sun is overhead at noon, sunlight has to travel a shorter distance through the earth's atmosphere to reach us. During this short journey of sunlight through the atmosphere, only a small amount of the blue light is scattered from the white light, keeping most of the white colour intact within it. However, at sunset or sunrise, the sun appears red because it is near the horizon, and sunlight has to travel a relatively longer distance through the earth's atmosphere to reach us. During this long journey, most of the blue colour is scattered from our line of sight. Therefore, the light reaching our eyes consists of the colour red of sunlight, which is of longer wavelength and is scattered the least.

Presbyopia is caused by a hardening of the lens of your eye, which occurs with aging. As your lens becomes less flexible, it can no longer change shape to focus on close-up images. As a result, these images appear out of focus.

Danger’ signls are red in colour because the red coloured light having longer wavelength is the least scattered by fog or smoke particles. Due to this the red light can be seen in the same colour even from a distance.

Violet light is refracted the most because violet colour has the minimum speed in glass prism.

Light-sensitive cells are present in the retina in abundance to be more specific the fovea centralis is the place of highest concentration.

The two most common defects of vision are myopia and hypermetropia. Myopia can be corrected by using a concave lens and hypermetropia can be corrected by using a convex lens.

The sky appears blue on a clear day because of the scattering of blue component of white sunlight by air molecules presents in the atmosphere. When sunlight passes through the atmosphere, most of the longer wavelength lights do not get scattered much and hence pass straight through the atmosphere. The shorter wavelength blue light is, however, scattered all around the sky and whichever direction we look, some of this scattered blue light enters our eyes.

The eye adjusts itself to deal with ight of vaying intensity with the help of the iris. The iris automatically adjusts the size of the pupil according to the intensity of light received by the eye. If the intensity of light is large, then iris contracts the pupil and reduces the amount of light entering the eye. And, if the inteintensity of light is small, then iris expands the pupil so that more light may enter the eyes.

As the person is wearing half-moon spectacles, he should be suffering from the eye defect called long-sightedness, or hypermetropia, because his spectacles are fitted with convex lens. The convex lenses form the images of nearby objects at the near point of his eye, and he can, therefore, see these objects clearly.

1. A and B,
2. D and E.

1. Myopia (Short – Sightedness).
2. Concave lens.

The innermost coating of the eye, covering the rear of inner surface is the retina. It is the screen on which the image is formed by the eye lens. Retina contains a large number of nerve fibres and blood vessels and act as a light sensitive screen to receive the images. The light sensitive cells get activated upon illumination and generate electrical signals. The sensation of vision in the retina is carried to the brain by optic nerve fibres, which are more than one million.

It's All about refraction. Not just we watch propelled dawn however additionally deferred sunset. This is on the grounds that when light enters from vacuum to earth's
air, It essentially enters from rarer to denser medium and twists towards skyline.
Amid dawn, when the sun is simply underneath the skyline, our environment causes the light.

Yes, it is possible to recombine the lights of seven colours to obtain the white light again by placing another similar prism alongside the first one in the inverted position as shown below. The first prism disperses the white light into seven coloured rays. the second prism receives all the seven coloured rays from the first prism and recombines them into original white light. This is because the refration produced by the second prism is equal and opposite to that produced by the first prism.

The refraction of light caused by the earth’s atmosphere is called atmospheric refraction. It is caused due to the varying optical densities of different layers of earth’s atmosphere.

1. The angle of deviation while passing through the the glass prism is maximum for violet colour since it has minimum wavelength.
2. The angle of deviation while passing through the glass prism is minimum for red colour since it has maximum wavelength.

1. Myopia: The type of lens used to correct Myopia is concave lens.
2. Presbyopia: An eye that suffers from myopia as well as from hypermetropia is said to suffer from presbyopia. A person with this defect cannot see objects distinctly placed at any distance from him. To correct this defect, a person is prescribed bifocal lens that has both types of lenses convex and concave.