Physics
Siphon will fail to work if:

The level of the liquid in the two vessels are at the same height.
Both its limbs are of unequal length.
The temperature of the liquids in the two vessels are the same.
The densities of the liquid in the two vessels are equal.

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Physics
Mirage is due to:

Magnetic disturbances in the atmosphere
Depletion of ozone layer in the atmosphere
Unequal heating of different parts of the atmosphere
Equal heating of different parts of the atmosphere

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