The higher and lower fixed points on a thermometer are separated by 150mm.When the length of the mercury thread above the Lower temperature is 30mm the temperature reading is??

To determine the temperature reading on a thermometer when the mercury thread above the lower fixed point measures 30 mm, we first need to understand how the thermometer is calibrated. The fixed points typically refer to the freezing and boiling points of water, which are often set at 0°C and 100°C, respectively. In this case, the total length between the higher and lower fixed points is 150 mm.

Understanding the Scale

The thermometer's scale is divided into two main fixed points: the lower fixed point (0°C) and the upper fixed point (100°C). The distance between these two points is 150 mm. This means that every millimeter on the thermometer corresponds to a specific temperature increment.

Calculating the Temperature Increment

To find out how much each millimeter represents in terms of temperature, we can use the following calculation:

• Temperature range = 100°C - 0°C = 100°C
• Length between fixed points = 150 mm
• Temperature increment per mm = 100°C / 150 mm = 0.6667°C/mm

Finding the Temperature Reading

Now that we know how much each millimeter represents, we can calculate the temperature corresponding to the 30 mm mark above the lower fixed point:

• Length of mercury above the lower fixed point = 30 mm
• Temperature reading = 30 mm * 0.6667°C/mm = 20°C

Final Temperature Value

Thus, when the mercury thread is at 30 mm above the lower temperature point, the temperature reading on the thermometer is 20°C.

Summary

In summary, by understanding the relationship between the physical length of the mercury column and the temperature scale, we can easily determine the temperature reading. In this case, a mercury thread length of 30 mm corresponds to a temperature of 20°C, illustrating how thermometers function based on fixed points and linear measurements.