PASCO TD-8551A MECHANICAL EQUIVALENT OF HEAT - Manual (Page 15)

012-04331E Mechanical Equivalent of Heat
11
Experiment: Measuring the
Mechanical Equivalent of Heat
Procedure
➁
It is often helpful to bring the cylinder down to several
degrees below the desired starting temperature. This
allows you time to determine the number of turns of
rope needed before actually taking data.
⑨
It is best to crank the cylinder as rapidly as possible.
This minimizes the time in which heat can escape to
the environment
Teacher’s Guide
Questions
➀ The accepted value of J is 4.184 Joules/calorie. It is
reasonable to expect results within 2% of this value.
(Typical results are J = 4.144 Joules/calorie)
➁
Some sources of error might be loss of heat to the en-
vironment, inaccurate measurement of temperature,
the fact that not all of the drum is aluminum (and thus
parts of it have a different specific heat), and nonuni-
form temperature in the drum. If the experiment is
done carefully, these are negligible.
➂ No. If the heat absorbed by the cylinder was more
than the work done on it, PASCO scientific would be
selling perpetual motion machines instead of real
physics apparatus. It is possible that students may
measure the heat as being more than the work done,
but this is experimental error.
➃
Not directly. There are many other factors that will
come into the calculations, including Carnot effi-
ciency.