Atmospheric pressure is measured by a

Options

A. doctor's thermometer
B. speedometer
C. mercury barometer
D. None of these

Answer

To solve the question "Atmospheric pressure is measured by a:", let's analyze the options provided and identify the correct instrument used for measuring atmospheric pressure.

### Step-by-Step Solution:

1. **Understanding Atmospheric Pressure**:
- Atmospheric pressure is the force exerted by the weight of air above a surface. It is a crucial concept in physics and is measured in various units such as Pascals, atmospheres, or millimeters of mercury.

2. **Analyzing the Options**:
- **Option 1: Doctor's Thermometer**: This instrument measures temperature, not pressure. Therefore, it cannot be used to measure atmospheric pressure.
- **Option 2: Speedometer**: This device measures the speed of a vehicle. It is unrelated to atmospheric pressure.
- **Option 3: Mercury Barometer**: This instrument is specifically designed to measure atmospheric pressure. It consists of a glass tube filled with mercury, where the height of the mercury column indicates the atmospheric pressure.
- **Option 4: None of these**: Since we have identified a correct option, this cannot be the answer.

3. **Identifying the Correct Answer**:
- Among the given options, the only instrument that measures atmospheric pressure is the **mercury barometer**.

4. **Conclusion**:
- The correct answer to the question "Atmospheric pressure is measured by a" is **Option 3: Mercury Barometer**.

### Final Answer:
Atmospheric pressure is measured by a **mercury barometer**.

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