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A loosely wound helix made of stiff meta...

A loosely wound helix made of stiff metal wire is mounted vertically with the lower end just touching the mercury in a dish. When the current from a batter is started in the metal wire through the mercury, the wire executes oscillatory motion with the lower end jumping out of and into the mercury. Explain.

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The windings of the metal helix carry currents in the same direction, therefore they experience attractive forces, pulling the lower end of metal wire out of mercury. When it happens, the circuit breaks, the current disappears and hence the force of attraction disappears. As a result of it, the wire helix regains its original position, completing the circuit again. The process is repeated time and again. Due to it, the oscillatory motion is set up.
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Torricelli was the first do devise an experiment for measuring atmospheric pressure . He took calibrated hard glass tube , 1 m in lengt and of uniform cross section , closed at one end . He filled the whole tube with dry mercury taking care than no air or water droplets remain inside the tube , closed the opposite end of the tube tightly with thumb and inverted it . He put this inverted mercury tube into a mercury through , taking care that the end of the tube remains inside the mercury through , An interesting thing was noticed . Mercury in the tube fell down at first and then stopped at a particular position . The height was 76 cm above the free surface of mercury in the through . When the given tube was inclined or lowered in the mercury trough , the vertical haight of mercury level in the tube was always found constant . Torricelli explained this by saying that the free surface of mercury in the trough . Hence , the hydrostatic pressure exerted by the trough measures the atmospheric pressure . If this expriment uses water instead of mercury , then

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