The drawing shows a conducting wire wound into a helical shape. The helix acts l

Question

The drawing shows a conducting wire wound into a helical shape. The helix acts like a spring and expands back toward its original shape after the coils are squeezed together and released. The bottom end of the wire just barely touches the mercury (a good electrical conductor) in the cup. After the switch is closed, current in the circuit causes the light bulb to glow. Does the bulb (a) repeatedly turn on and off like a turn signal on a car, (b) glow continually, or (c) glow briefly and then go out?

The drawing shows a conducting wire wound into a helical shape. The helix acts like a spring and expands back toward its original shape after the coils are squeezed together and released. The bottom end of the wire just barely touches the mercury (a good electrical conductor) in the cup. After the switch is closed, current in the circuit causes the light bulb to glow. Does the bulb (a) repeatedly turn on and off like a turn signal on a car, (b) glow continually, or (c) glow briefly and then go out?

Explanation / Answer

a)

When the current is flowing in the coil (spring),it does so in a way that current in every pair of adjacent turns flows in same direction.As a result there will be an attractive force between any pair of turns with total force being compressive in nature.This contracts the spring and it loses contact with mercury and circuit becomes open.When no current flows through spring, the force no more acts.As a result the spring relaxes back and establishes contact with mercury.This goes on continually and the result Will be that bulb glows intermittently.

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