Physics
Superconductors are substances which

conduct electricity at high temperatures
offer high resistance to the flow of current
conduct electricity at low temperature
offer no resistance to the flow of electricity

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Physics
The blue colour of sky is due to

Scattering of shorter wavelengths of sunlight in the atmosphere
Refraction of sunlight
Scattering of longer wavelengths of sunlight in the atmosphere
Reflection of sunlight

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