WHITE LIGHT
INTRODUCTION
We need a source of white light to make any object visible. When light falls on any object, we can easily see this even in the dark. If light comes from an object in what is white light and it enters into our eyes through which we can see the object. So, object either must emit light or getting reflected by light to make the object visible. According this phenomenon, there are two types of objects.
LUMINISITY OF OBJECTS
LUMINOUS OBJECT:
Object which emits their own light that we term as luminous object, like the sun, electric bulb, burning candle etc.
NON-LUMINOUS OBJECT:
Objects which do not emit their own light that we term as non-luminous object, like the moon, the earth, wood etc.
SUNLIGHT : WHITE OR COLORED
Since, the sunlight we term as white light. The sunlight actually consists of seven colors. White light splits into seven colors when passing through a transparent medium like a glass prism. This event in what is white light ,we term as dispersion of white light. Prism is a piece of solid glass which breaks up the sunlight into its seven colors like V (violet) ; I (Indigo) ; B (Blue) ; G (Green) ; Y (Yellow) ; O (Orange) ; R (Red) .
QUESTION ANSWER ON WHITE LIGHT
VERY SHORT QUESTIONS
Qs1: Mention the seven English letters that do not show lateral inversion on suffering reflection from a plane mirror.
Ans1: The seven English letters not showing lateral inversion after reflection in plane mirror are H, I, A, M, O, U, T.
Qs2: What are the functions of rods and cones in our eyes in white light?
Ans2: Rods are sensitive to dim light so it helps in dim light or dark vision. Cone cells are sensitive to the bright white light so it helps in bright vision or color vision.
Qs3: Mention the range of vision of a normal human eye.
Ans3: Human normal eye vision ranges from 25 cm (near vision) to infinity (far vision) in white light.
ANSWER IN BRIEF IN WHITE LIGHT
Qs4: State in brief about angle of incidence and angle of reflection.
Ans4: The incident ray and the normal forms incident angle. The reflected ray and normal forms reflection angle. According to snell’s law, both angles are equal in measurement in what is white light.
Qs5: If someone is having cataract, then which part of eye is having problem? What is the treatment?
Ans5: If people suffering from cataract, there is opaqueness or cloudy appearance in the eye lens where white light cannot reach.
Doctor can treat this by removing the cloudy lens with a new artificial lens.
Qs6: Explain how do ciliary muscles affect the working of the eyes?
Ans6: Ciliary muscle has ability to contract and relax. In this way they can change the focusing of eye lens followed by change of focal length. Hence, eye lens can make image of nearby objects and also far off objects on retina.
CONCEPTUAL QUESTIONS IN WHAT IS WHITE LIGHT
Qs7: Nocturnal birds have large cornea and pupil in their eyes. How do they get help from these structures?
Ans7: Eyes of nocturnal birds are large in size. So they do have wider pupil with large lens and big surface area of retina. These help can collect adequate amount of white light light. It helps to see the objects in the dark night.
Qs8: Differentiate between surfaces of sandpaper sheet and a mirror.
Ans8:
| CHARACTERS | SURFACE OF SANDPAPER SHEET | SURFACE OF MIRROR |
| TYPE | Rough | Plain |
| REFLECTION | Scattered | Regular |
| IMAGE | No image is formed | Sharp image is formed |
Qs9: State in which way we can see the objects in white light?
Ans9: We can see various objects due to reflection. Though we know, all types of surfaces reflect white light. So, when light falls on any objects, it reflects regular or irregular way. In this way, our eyes catch the reflected eyes. In this way we can see the objects.
ANSWER IN BRIEF IN WHAT IS WHITE LIGHT
Qs10: The distance between an object and a convex lens is changing. We know that the image size decreases ? What is the reason behind it?
Ans10: If we move the object far away from the convex lens, the size of image decreases. There is a point image at the focus if the object is placed at infinity.
Qs11: We place two different lenses on a newspaper sheet. How can you identify the lenses without touching?
Ans11: We can differentiate the lenses by identifying the letters of newspaper. When we observe large or magnified letters through which lens , that lens is convex. If the letters are smaller and diminished in size through which lens, that one is concave.
HIGHER ORDER THINKING QUESTIONS IN WHITE LIGHT
Qs12: Suppose the reflecting surface of a torch which is concave gets rusted. Which effect would you see on the light beam coming from torch?
Ans12: Rusted reflecting surface of torch produces diffused white light with very low intensity. So, we cannot see the objects clearly due to diffused and lower intensity.
Qs13: A shopkeeper wants to get maximum view of his shop. So, he wants to fix a mirror. Explain, which type of mirror should he fix?
Ans13: He must use convex mirror. By this mirror, he can get maximum view of his shop. Convex mirror gives a wider field of view. This mirror can collect light from a large area from the shop which helps to visualize maximum area of the shop.
Qs14: In ambulance the vehicle name is written laterally inverted. Why?
Ans14: Mirror forms laterally inverted letters that means left seems in right position and right seems in left position. The ambulance is an emergency vehicle carrying patients to reach hospital very fast. Other vehicles drivers can see the ambulance from the rear view mirror. In this way they can easily identify the emergency of ambulance and gives the ambulance way.
Qs15: There must be a shiny and smooth surface for white light reflection?. Justify the statement.
Ans15: Light reflection depends upon two factors, shine and smoothness of the surface. If the shining and smoothness of the surface are increased, then sharpness of the reflection is increased. That is why we need a shiny and smooth surface for better reflection.