Question

A water tank is 4 metre deep. A candle flame is kept 6 metre above the level. Where will the image of the candle be formed ?
μ for water is 4/3.

Answer 1

A water tank is 4 m deep , A candle flame is kept 6m above from the ground level as shown in figure. so, candle flame is 2m above from water level.

According to rule ,
Refractive index of water = height of image of candle from water level/height of candle from water level .
From figure it is clear that ,
Height of image from water level is (h + 2)m
Height of candle from water level is 2m
And refractive index of water is μ = 4/3
so, μ = 4/3 = (h + 2)/2
(h + 2) = 8/3 = 2.67 m

Hence, image of candle from water level is 2.67 m
Or image of candle from Ground level is (4 + 2.67) m = 6.67m

Answer 2

The correct answer should be approx. 6 meters.

The image of the candle will be formed by refraction. So, the refractive index of the medium should be considered.

The question says that the water tank is 4 metres deep and the candle flame is kept at a height of 6m above that level. Therefore, the actual height of the candle flame that is above the water level is 2metres.
By applying the equation, Refractive index (μ) = H1/H2

So, Refractive index (μ) of water = (h + 2)/2 (since the distance between the 2 heights is 2 meters).

μ = 4/3 = (h + 2)/2 

(h + 2) = 8/3 ~ 2.67 m 
So, the image of the candle is formed at approx. 2 meters from the water level.

So, the image of the candle will be formed at (4 + 2) m = 6 m from the ground level.