Question

Two thermometers are constructed in the same way except that one has a spherical bulb and the other a cylindrical bulb; which one will respond quickly to temperature changes?

• A. Spherical bulb thermometer
• B. Cylindrical bulb thermometer
• C. Both equally
• D. Either of any option

Answer 1

The correct option is B Cylindrical bulb thermometer

The rate of flow of heat through conduction is given by
$\frac{dQ}{dt}=\frac{KA({\theta }_H-{\theta }_L)}{d}$
In order that a mercury thermometer inspite of having low thermal conductivity (K) of glass may quickly conduct heat from a body to mercury; the glass bulb containing mercury is made long (so that its area is increased) and thin (so that d is decreased).
Hence, the correct answer is option (b).