NCERT Class XII Chapter
Ray Optics and Optical Instruments
Questions With Solutions
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Question : 3
Total: 38
A tank is filled with water to a height of12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be 9.4 cm. What is the refractive index of water? If water is replaced by a liquid of refractive index 1.63 upto the same height, by what distance would the microscope have to be moved to focus on the needle again?
Solution:
We know the relation
Apparent depth =
9.4 cm =
µ ω
Now if the water is replaced by other liquid, the apparent depth will change and microscope will have to be further moved to focus the image.
With new liquid
Apparent depth =
Now the microscope will have to shift from its initial position to focus on the needle again which is at 7.67 cm depth.
Shift distance = 9.4 – 7.67 = 1.73 cm.
Apparent depth =
9.4 cm =
Now if the water is replaced by other liquid, the apparent depth will change and microscope will have to be further moved to focus the image.
With new liquid
Apparent depth =
Now the microscope will have to shift from its initial position to focus on the needle again which is at 7.67 cm depth.
Shift distance = 9.4 – 7.67 = 1.73 cm.
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