Explain the working principles of a clinical thermometer and a hydrometer.

Here's how these measuring instruments work:

a) Clinical thermometer
A clinical thermometer works on the principle of thermal expansion. It contains a liquid (usually mercury or alcohol) in a bulb connected to a narrow capillary tube. When the bulb is placed in contact with the body, the liquid absorbs heat and expands, rising up the capillary tube. A calibrated scale indicates the temperature. It has a constriction (kink) near the bulb that prevents the liquid from falling back immediately after removal, allowing time for an accurate reading.

b) Hydrometer
A hydrometer works based on Archimedes' principle of buoyancy. It is a sealed glass instrument with a weighted bulb at the bottom and a long, narrow stem with a calibrated scale. When placed in a liquid, it floats. The depth to which it sinks depends on the density of the liquid. It sinks deeper in less dense liquids and floats higher in more dense liquids. The reading on the scale at the liquid's surface indicates the relative density (or specific gravity) of the liquid.