9.Why is expansion of mercury in a thermometer considered as a reversible change?
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Answers
Answer:
The mercury-in-glass or mercury thermometer was invented by physicist Daniel Gabriel Fahrenheit in Amsterdam (1714).[1] It consists of a bulb containing mercury attached to a glass tube of narrow diameter; the volume of mercury in the tube is much less than the volume in the bulb. The volume of mercury changes slightly with temperature; the small change in volume drives the narrow mercury column a relatively long way up the tube. The space above the mercury may be filled with nitrogen gas or it may be at less than atmospheric pressure, a partial vacuum.
Answer:
Explanation:
Expansion and contraction
Substances expand (increase in size) when they get warmer, and they contract (decrease in size) when they get cooler. This property can be useful. For example:
Thermometers work because the liquid inside them expands and rises up the tube when it gets hotter.
Metal parts can be fitted together without welding, using shrink fitting. The slideshow shows how this works:
The rod is too large to fit through the hole
Bridge expansion joint.
Expansion joints like this allow bridges to expand and contract without damage
The expansion and contraction of materials can also cause problems. For example, bridges expand in the summer heat and need special joints to stop them bending out of shape.
What do the particles do?
When substances expand or contract, their particles stay the same size. It is the space between the particles that changes:
the particles in a solid vibrate more when it is heated, and take up more room
the particles in a liquid move around each other more when it is heated, and take up more room
the particles in a gas move more quickly in all directions when it is heated, and take up more room
Compares particles in a solid when cold and when hot. When the particles are cold, they are closer together and vibrate less. When they are hot, they vibrate more and are further apart
The space between particles changes when a substance expands (or contracts)
Remember, the particles themselves never expand.