Why does the mercury level not fall on its own when the bulb of a clinical thermometer is removed from the mouth ?

Explanation

### Step-by-Step Solution

1. **Understanding the Thermometer Structure**: A clinical thermometer consists of a glass tube with a bulb at one end filled with mercury (or colored alcohol). This bulb is designed to expand when heated, causing the liquid to rise in the tube.

2. **Removing the Thermometer**: When the thermometer is removed from the mouth, the heat source (the body) is taken away. Normally, one would expect the mercury to fall back down the tube due to gravity.

3. **The Role of the Kink**: Inside the thermometer, there is a specific feature known as a "kink." The kink is a constriction or narrow part of the tube that prevents the mercury from flowing back down immediately.

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