Askiitians Tutor Team
Last Activity: 2 Days ago
To understand how a mercury thermometer can accurately measure the temperature of a hot body, even when it initially has a different temperature, we need to delve into the principles of thermal equilibrium and the properties of the materials involved.
The Basics of Thermal Equilibrium
When two objects at different temperatures come into contact, heat will flow from the hotter object to the cooler one until they reach a state of thermal equilibrium. This means that the temperatures of both objects will equalize. In your scenario, we have a hot body at temperature T and a mercury thermometer at a lower temperature, tk.
How the Mercury Thermometer Works
A mercury thermometer consists of a glass tube filled with mercury, which expands and contracts with temperature changes. When the thermometer is placed in contact with the hot body, heat transfers from the hot body to the mercury. This causes the mercury to expand, moving up the scale of the thermometer.
Understanding the Temperature Reading
Initially, the thermometer is at temperature tk, which is less than T. As heat flows into the thermometer, the mercury's temperature rises. The key point here is that the thermometer does not instantly measure the temperature of the hot body; instead, it gradually adjusts to the temperature of the hot body.
Why the Final Reading is Accurate
When thermal equilibrium is reached, the temperature of the mercury (let's call it T3) will equal the temperature of the hot body (T). This is because the thermometer is designed to respond to the temperature of the environment it is in. The reading on the thermometer reflects the temperature of the hot body at the moment equilibrium is achieved.
Factors Influencing Accuracy
- Material Properties: Mercury has a high thermal conductivity, allowing it to quickly reach thermal equilibrium with the surrounding environment.
- Calibration: Thermometers are calibrated to ensure that the scale accurately reflects temperature changes based on the expansion of mercury.
- Response Time: The design of the thermometer affects how quickly it can respond to temperature changes. A well-designed thermometer will minimize lag time.
Conclusion on Measurement Accuracy
In summary, while the mercury thermometer starts at a lower temperature than the hot body, it accurately measures the temperature of the hot body once thermal equilibrium is reached. The final reading reflects the temperature of the hot body because the thermometer is designed to respond to the heat transfer until both the thermometer and the hot body are at the same temperature. This process ensures that the thermometer provides a reliable measurement of the hot body's temperature.
