Question

What is the use of kink near the bulb in a clinical thermometer
A. It prevents the level of mercury from falling when taken out of the mouth
B. It allows the level of mercury to fall when taken out of the mouth
C. It allows the level of the mercury to rise when taken out of the mouth
D. It prevents the level of the mercury from rising when taken out of the mouth

Answer 1

Hint: The level of mercury can rise and fall quite rapidly through a thin capillary tube and cause error in reading. A kink hinders the flow, making it slow.

Complete step by step answer:
A clinical thermometer is used to measure the temperature of the human body. It shows both Celsius (C) and Fahrenheit (F) temperature scales. Its temperature scale runs from 35 C to 42 C (95 F to 110 F). The stem of the thermometer consists of a thin capillary tube. The capillary tube is scaled to show the temperature. At the end of the tube, there is a bulb that contains the mercury. The volume of mercury changes by 0.018% for every degree change in temperature. This may seem very small, however when it expands through the thin capillary tube of the thermometer, the level can rise or fall quite fast. Now, to prevent the sudden fall in the level of mercury after a temperature is measured and causing error in the reading, the thermometer is provided with a kink near the bulb. The kink regulates the in and out flow of mercury from the bulb, making the rise and fall in level of mercury in the tube slow. As such it takes more time to reach a given temperature marking, and also doesn’t fall rapidly as the temperature starts falling. Therefore, the kink near the bulb in a clinical thermometer prevents the level of mercury from falling when taken out of the mouth.
Hence the correct option is A.

Note:
Without the kink, it would be impossible to get a correct reading of the temperature, as the level would change rapidly.