Physics
Which of the following principle is used to produce ''low-temperatures' ?

Super conductivity
Joule-Kelvin effect
Thermo-electric effect
Adiabatic demagnetisation

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Physics
Stationary wave is formed by

Two waves of same frequency travelling in the opposite direction
Two waves of same frequency travelling in the same direction
A transverse wave superposing a longitudinal wave
Two waves of the same speed superposing

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Physics
An electron microscope gives higher magnification than an optical microscope, because :

It uses more powerful lenses
The wavelength of electrons is smaller as compared to the wavelength of visible light
The electrons have more energy than the light particles
The velocity of electron is smaller than that of visible light

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