Physics
Siphon will fail to work if:

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

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Physics
Mirage is due to:

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

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