Question

Describe to errors in Linear Expansion Experiment and suggest solutions to solve them.

Answer 1

In Linear expansion experiment, the linear expansion of metal rods of different materials (atleast two, generally Aluminium and Copper) due to increase in temperature is studied. From the experiment it is verified that change in length of the metal tube is directly proportional to the change in temperature of the tube and the co-efficient of linear expansion of these metal rods are determined as per the following formula:

where,

original length at room temperature

= length of the rod at a higher temperature

= Change in length of the rod

= Change in temperature

All the above parameters are to be measured in the experiment and are, thus, the possible sources of error in this experiment. The room temperature and other higher temperatures are measured with the help of thermistors attained to the metal tube. Multimeters are used to record the change in resistance of the thermistor which is further corelated with the temperature rise from a standard data sheet or directly temperature is recorded from a temperature meter.

Dial gauge is used to record the change in length. Normally, the dial guage is observed and recorded for a change in length of 1.00 mm.

Potential sources of error:

1. Before starting the experiment, it should be ensured that there is no condensed water in the tube. If there remains some water in the tube, there will be a heat transfer beween the water and the steam and the percentage deviation between the experimental and theoretical value of the linear coefficient of the metal rods will be more.

Solution: The tube should be drained out completely before starting the experiment.

2. The laboratory should be too low compared to the outside room temperature which often is the case of an air conditioned laboratory where the temperature is maintained below the actual room temperature. The cold temperature inside the room makes the metal cool faster than normal temperature.

Solution: No air conditioning should be used in the laboratory while performing the experiment.

3. Loosely inserted leads inside the thermistor connection terminals: Due to loose leads, a slight movement of the wires causes a sudden change in the resistance recorded by the multimeter, leading to inaccurate readings of resistance and hence the temperature change.

Solution: The leads should be tightly inserted into the thermistor connection terminals and the measuring wires should not be moved during the experiment.

4. Wrong measurement of the dial gauge: If the dial gauge stopped moving during the experiment otherwise thethe gauge will record wrong expansion.

Solution: The dial gauge should be regularly monitored during the experiment.

Regards,

5. Personal error is always a potential source of error. When measurement of length is done witht a meter stick, it should be ensured that the length is measured to its nearest multimeter to lessen the error. The measurement of change in resistance or change in temperature should be done precisely.

Solution: Experiment should be done with full concentration.