An Example Lab Report (Page 3 of 5) in pdf

An acoustical transducer was attached to each end of the bar under investigation. A pulse

was applied to one end and a digital timer was used to determine how long it took for the

wave to travel down the bar to the pickup transducer. As each bar was one meter long,

the velocity in meters per second is simply 1/time delay. The bar was then placed in an

industrial oven and the measurement repeated at temperatures of 75C and 125C to

compare to the nominal room temperature (25C) results.

The room temperature results agreed strongly with the published data of the three

materials. Comparing Table 1.1 to the 25C column of Table 1.2 showed a deviation no

worse than 1.64% (final column, Table 1.2). The variation between materials is

approximately 3:1, indicating how strongly the internal characteristics of the material

influence the speed of propagation. The CCCD material, being the most plastic, should

have the greatest internal frictional losses, and thus, the slowest velocity of the group.

This was the case. The inclusion of porcupinium in the SB alloy was responsible for the

modest velocity of this material. The waves have to propagate relatively slowly through

the porcupinium compared to the GA alloy which is free of this ingredient. The speed of

propagation for all materials was significantly faster than the speed of sound through air.

Even the slowest of the group, CCCD, exhibited a velocity nearly three times that of air.

The temperature coefficients also showed tight agreement, and appear to be within just a

few percent of the established values. Generally, the velocity increases with temperature,

although the GA alloy produced the opposite affect. It is assumed that the inclusion of

kryptonite in the alloy may be responsible for this. See Graph 1.1 for details.

There was a practical issue involving the CCCD material. The measurements at 25C and

75C were satisfactory, however, when the CCCD bar was removed from the 125C oven it

had changed texture and color to a crispy golden brown and produced a strong, pleasing

odor. Consequently, one member of the lab group ate approximately 10 centimeters of

the bar before the velocity could be measured. To correct for this, the measured time

delay was adjusted by a factor of 1.11 as the bar had been reduced to 90% of its original

length.

An Example Lab Report Page 3