1. Why does the sun look a little oval when it is on the horizon?
Solution: When the sun or the moon is near the horizon, the rays from the longer edge are refracted more.
Because they traverse a greater thickness of air in comparison to the rays from the upper edge.
Thus the vertical diameter appears to be shortened while the horizontal diameter remains unaffected.
Hence the disc of the sun or the moon does not appear to be circular but seems to be slightly flattened/ elliptical/or oval.
Another reason is that when the sun is near the horizon, its rays have to travel a longer distance than at noon.
On account of greater refraction, the size of the sun appears to be longer in the former case than in the latter case.
2. Why do two eyes give better vision than one?
Solution: The area seen clearly with one eye is comparatively less (approximate range 135°) than with two eyes (range 180°).
Two eyes also give better judgment of distances of different objects.
The left eye sees more of the object's right side, and the right looks more like the left side.
Thus two eyes do not form exactly similar images, and the fusion of these two different images in the brain gives the three-dimensional stereoscopic vision.
3. Why do figures on the screen appear to be moving in a cinema show, even though the pictures on the film are still (i.e., steady)?
Solution: The sensation of light, as interpreted by the brain, persists for a brief interval after the actual light stimulus is removed. Successive images, if they follow one another sufficiently rapidly, produce a continuous impression.
That is why figures on the screen appear to be moving in a cinema show even though the pictures on the film are still.
4. Why does the setting sun appear red as it approaches the horizon?
Solution: The setting sun appears red as it approaches the horizon due to the scattering of light by very minute particles of dust or smoke near the earth's surface.
At noon, the sun is overhead, whereas it is near the horizon at the time of sunrise or sunset.
A ray of light has to cover a greater distance through the atmosphere in the latter case. Component colors of sunlight have different wavelengths.
The minute dust particles suspended in the air can scatter short wavelength colors only like blue and violet. In contrast, the red color of a more extended wavelength can pass through the atmosphere unscattered.
Hence the setting sun appears red.
5. Why does a green leaf appear green in daylight but dark in red light?
Solution: A green leaf appears green in daylight because it absorbs all the constituent colors of white light except green which is reflected in us.
The green leaf appears dark when viewed in red light because it can absorb all colors except green.
As red rays falling on the leaf are absorbed by it, it will appear dark.
6. Why is rose red and grass green in daylight?
Solution: A rose appears red when daylight falls on it because it absorbs all the constituent colors of white light except red, which it reflects before us.
Similarly, grass absorbs all the constituent colors of white light except green, which is reflected before us.
Therefore, a rose appears red and grass green to us.
7. What will be the color of grass in blue light?
Solution: Grass will appear dark in color in blue light because it has the property of absorbing all other colors except its color.
The blue rays falling on grass are absorbed by it, and hence it appears dark in color.
8. The color of the same cloth, when seen in electric light, appears different from the paint when seen in daylight. Why?
Solution: When a body is viewed in daylight, it reflects some color called its natural color. Electric light, on the other hand, is not pure.
It may be deficient in some colors or has got some particular color in excess.
This is why objects sometimes appear to be of a different color in artificial light from their natural color, which they show in white light.
9. Why a dark blue suit appears black when viewed in candlelight?
Solution: Candlelight is deficient in blue color, whereas yellow paint is in excess in it.
When yellow light falls on the blue suit, the blue color is absorbed by it, and hence the appearance of the case is black.
10. Why do motorists use a convex mirror to see the road behind them?
Solution: Convex mirrors are always used by motorists to view the traffic behind the car.
The image formed by a convex mirror is always diminished in size, erect and thus producing a large field of view.
It may be noted that with the help of a convex mirror only, it is not always possible for the driver to get a correct idea about the size and distance of the object behind the car
because the image formed is diminished in size and lies between the focus and the pole of the mirror.
A plane mirror is, therefore, fixed along with a convex mirror to get the correct view of the size distance of the object.
11. Why does a straight stick look bent when partly immersed in water?
Solution: This illusion is caused due to the phenomenon of refraction.
When a stick is partly immersed in water, the rays of light starting from the lower end of the post, after traveling through water, strike the surface of separation (water and air)
and bend away from the classic look because air is an optically rarer medium.
Thus the rays appear to diverge from a point higher than the actual position.
Hence, when the stick is viewed from above the surface of a vessel or from the side through the water in a glass vessel, it appears to be broken at the feeling of separation of water and air.
12. Why is the sound heard a little after the smoke is seen when a gun is fired within a visible distance?
Solution: The velocity of light is much greater than that of sound. In other words, light travels faster than sound.
Therefore, the flash of lightning or smoke of the gun is seen before the thunder of lightning or the sound of the gun being fired.
13. Why is the rainbow seen after rain?
Solution: After the rain, some clouds linger in the sky, containing water droplets.
Water droplets act like prisms. Sun's rays' falling on water droplets suffer dispersion and produce a spectrum. Hence the different colors are viewed in the form of a rainbow.
14. Why the sky appears blue?
Solution: Minute dust particles and water vapors always remain suspended in the atmosphere. In the sun's light, blue and violet waves are of smaller wavelengths.
And these are quickly scattered or reflected by the water vapors and dust particles present in the atmosphere, whereas long wavelengths of other colors can not pass through them.
A dust particle cannot reflect a wavelength more significant than its size. As blue color is of short wavelength and is scattered and thus makes the sky appear blue.
15. What is meant by Persistence of Vision?
Solution: The sensation of light, as interpreted by the brain, persists for a brief interval after the actual light stimulus is removed.
(i.e., our eye continues to see the image of the object for about 1/10th of a second, even when the thing is removed from view).
This is known as 'Persistence of Vision.' Successive images, if they follow one another sufficiently rapidly, produce a continuous impression.
This principle is made use of in cinematography. A series of still pictures are projected on a screen at the rate of 20-24 shots per second.
The images formed on the screen hurry that an impression of a motion picture is conceived.
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