4. A coin is kept at the bottom of an empty bucket. A student standing near to it cannot see
the coin. Another student pours some water into the bucket without disturbing the coin
Now, the first student is able to the see the coin from the same position.
a) Explain how it becomes possible to see the coin now?
b) Draw a ray diagram to justify your answer.
Answers
Answer:
(a)The portion of light reflected greatly depends on the incident angle made by the incident ray on the object. If the light goes almost parallel to the surface then it will reflected almost completely. So if you stand and look straight down into the bucket then the reflection of coin placed into a bucket will not get brighter reflection and hence you will unable to see the coin.
Now when coin is kept into the bucket with water the light that passed through eventually disperses and does not come back. As a result all one can see in that case is the reflected light. This makes the coin visible placed into the bucket of water.
Moreover, when coin is placed into the bucket of water and when the student straightly looks down into the bucket then as the refractive index of water is greater than that of air, therefore the coin will look closer. This is known as apparent depth of the coin which depends upon the refractive index of the water and mathematically given as,
h'=hn2n1h'=hn2n1
where, n1 is the refractive index of air and n2 is the refractive index of water.
Answer:
Due to the refraction of light in water, the first student is able to see the coin. water being denser than air bends the light inwards inside the bucket and thus the coin is visible.