Calibration curve of a thermometer using a mercury thermometer as a standard
An unmarked thermometer (alcohol in this expt.) can be calibrated using a mercury thermometer as a standard. Both thermometers are placed in melting ice (0 degrees C), the length of the alcohol "thread" is noted. A heater is switched on causing the water temperature to gradually increase. For at least six temperature values the corresponding length of the alcohol thread is noted. A graph of length of alcohol thread against temperature is the required calibration curve.
Procedure:
- Familiarise yourself with the scale on the thermometer and on the ruler. Note the starting temperature and the length of the alcohol thread. Record in a table as shown below.
- Press " Apply Heat".
- As the temperature increases note the temperature and the corresponding length of the alcohol in the unmarked thermometer at least six times
- The hotplate stops automatically when the temp. reaches 100 degrees Celcius. If you want to repeat the experiment press "Reset" and repeat steps 2 and 3
Analysis:
Plot a graph, on graph paper, of length of alcohol thread (y-axis) against temperature. Any temperature between 0 and 100 degrees can now be measured using the unmarked thermometer. Place it in a beaker of moderately hot water, measure the length of the alcohol thread and, from the calibration curve, read the corresponding temperature.
Precautions:
- Place both thermometers in melting ice (0 deg. C) for a few minutes at the start of the experiment.
- Heat the water very slowly so that it is easy to take temperature and length readings simultaneously
- Have your eye level with the liquid columns when taking temperature and length readings to avoid parallax errors
