Pasco TD-8551A MECHANICAL EQUIVALENT OF HEAT Manuel d'utilisateur télécharger pdf (Page 15)

012-04331E Mechanical Equivalent of Heat

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.

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Pasco TD-8551A MECHANICAL EQUIVALENT OF HEAT Manuel d'utilisateur Page 15