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NAEST 2020 The intensity of Bucket s Image formed by Floor T

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Question: In the video, the intensity of the image decreases as the camera goes closer to the bucket. The reason for this behavior is

  1. The intensity of the reflected light increases with the angle of incidence in the given range of angles.
  2. The intensity of light from an object decreases as it moves away from the object.
  3. Law of reflection i=r is not valid for a tile which is an opaque object.
  4. Bucket diffracts light which has more intensity in directions closer to horizontal.

Solution: Let us try to understand the quality of an image formed after reflection. Let us think about a candle, a concave mirror, and an image of the candle formed on a screen.  The image formed is usually blurred. You can make it sharp by moving the screen (towards or away from the mirror).

The image is sharp if light emanating from one point of the candle reaches only one point of the screen. There is one-to-one correspondence between points on the candle and points on its image on the screen. Now, if you move the screen, the light from one point of the candle reaches multiple points on the screen and the image becomes blurred.

Let us do the same experiment in two environments (i) in a dark room and (ii) in sunlight. You can easily see the image in a dark room but the image is hardly visible in the sunlight. Why? It has to do with the surrounding (or contrast). Have you ever thought about why you cannot see the stars in the day? For us to see an object (or image), the intensity of light reaching our eyes from the object (or image) shall be distinct from the light reaching our eyes from the surrounding. Think over it!

Now, let us come back to the bucket and its image. The image is sharp when we are looking from a distance. The light emanating from the bucket gets reflected by the floor's tiles. A part of this reflected light enters our eyes. When looking from a distance, the light reflected from a large floor area enters our eyes. The intensity of light entering our eyes after emanating from the bucket and reflection from the tiles is much larger than the light entering our eyes from the surrounding. The intensity of bucket's light that enters our eyes is more when the angle of incidence is large (because light reaches our eyes from a larger floor area). This is not the case when we move closer to the bucket. The image faded away due to poor contrast. 

Thus, option (A) seems to be most appropriate.

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