Immagini

DESCRIPTION

Exhibit 693 is a simple apparatus designed by Ritchie to study phenomena of emission and absorption of radiant heat and to demonstrate that a good absorber of heat is also a good emitter.

The apparatus has a rectangular wood base with four wood feet. There are two empty metal cylinders (B) and (C) connected by a glass tube bent twice at right angle and containing some liquid (for example, sulfuric acid) that form a differential air thermoscope (see design-1). Between (B) and (C) there is another small cylinder (A) that can be filled with boiling water and closed with a tap, shifted horizontally along a scale and rotated around a vertical axis. The three cylinders are aligned and mounted so that their bases are vertical. Each cylinder has one base shiny and the other base blackened.

There are two vertical wood scales along the glass sections of the bent tube (L) and (M) graduated from -90 to +90 mm. A brass scale graduated in cm from -7,3 to +7,3 is located halfway between (B) and (C) to indicate the position of (A).

The experiment has two phases. In the first, the darkened face of (C) is oriented toward the shiny face of (A) and the shiny face of (B) is oriented toward the darkened face of (A). Upon pouring boiling water in (A), there is no effect visible on the liquid in the tube (LM). Upon rotating the cylinder (A) 180° the column of liquid lowers in (M) and rises in (L) due to the heating in (C). Thus when the darkened face of (C) sees the darkened face of (A) there is more heat transmitted between (A) and (C) than between (A) and (B) that have shiny faces looking at each other. Thus it has been demonstrated that good absorbers are also good emitters.

In the museum there is a similar apparatus in exhibit 694.

BIBLIOGRAPHY

• [1] Giovanni Boato, Giuseppe Bruzzaniti,"Strumenti nella fisica dell'ottocento",pag-130, SAGEP, 1993
• [2] Abdul Basir PAL, “Elementary Physics", 5th edition, 1956, Page 281,M.R. Brothers, Lahore, Pakistan.
• [3] Sutton, "Demonstration Experiments in Physics", Part-III, § H163, P-241
• [4] Ritchie's Illustrated Catalogue of Physcal Instruments and school apparatuse office, 150 tremont street, Boston 1878 pag. 42 N. 430

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