Bottom of a tank containing water appears to be raised. It is due to
- A.Reflection of light
- B.Refraction of light
- C.Interference of light
- D.Diffraction of light
Correct answer
Explanation
The correct answer is B, Refraction of light. Light from the bottom bends as it passes from water into air, so the bottom seems nearer than it really is.
Water is optically denser than air. A ray leaving the tank floor bends away from the normal at the water surface, and our eye traces it back along a straight line to a point above the real floor. The apparent depth equals the real depth divided by the refractive index of water, about 1.33, so a tank looks only about three quarters as deep as it is. The same bending makes a straight stick look bent where it enters water.
A is wrong because reflection sends light back into the same medium, as in a mirror, and does not change apparent depth.
C is wrong because interference is the overlap of light waves, seen in soap films and oil patches.
D is wrong because diffraction is the spreading of light round small edges and slits.
Exam tip: apparent depth = real depth ÷ refractive index; it explains raised tank floors and bent sticks.
Practice Questions
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- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
Show answer
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Read the full explanation →Which set of vegetables is underground stem or modified stem of a plant?
- A.Potato, artichoke, round gourd
- B.Onion, garlic, carrot
- C.Potato, onion, garlic
- D.Potato, garlic, turnip
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All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.
Read the full explanation →A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :
- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
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A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.
Read the full explanation →A body floats in a liquid if the buoyant force is :
- A.equal to its weight.
- B.less than its weight.
- C.greater than its weight.
- D.zero.
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A floating body is in equilibrium, so the upward buoyant force exactly balances its weight. By Archimedes' principle, a body in a liquid is pushed up by a force equal to the weight of the liquid it displaces.
Read the full explanation →Which of the following are the different parts of a human brain ?
- A.Forefront brain, Standard brain and Hind brain
- B.Fore brain, Median brain and Rear brain
- C.Fore brain, Mid brain and Hind brain
- D.Precursor brain, Mean brain and Hind brain
Show answer
These are the three main divisions of the human brain. The fore brain is the largest part.
Read the full explanation →