EXPERIMENTAL: AN INVESTIGATION INTO SOME OF THE VARIABLES INVOLVED IN 
THE ABSORPTION AND/OR EMISSION OF RADIANT HEAT ENERGY

Introduction
Radiant heat energy, in the form of electromagnetic waves, is emitted
from hot bodies (e.g., the Sun, light bulbs, and living organisms). A 
detailed knowledge of the variables which affect the absorption and the
emission of this energy is necessary to understand various phenomena,
including 'homeostasis in ectotherms', 'photochemical reactions', and 
'the detection of prey by certain predators (e.g., snakes)'.

The amount of radiant energy absorbed by a surface is well known to be
affected by a number of independent variables; these include the total
and type of energy emitted from the heat source, the distance of the 
surface from the source, the colour of the surface, and its lustre
(i.e., whether the surface is shiny or dull). However, there appears 
to be relatively few details concerning the quantitative relationships 
between possible variables - though four are summarized in Note 1.

In this investigation, you are required to examine at least four
variables involved in the absorption and/or emission of radiant heat 
energy; at least three of the variables must be quantitative, and at
least one must be qualitative.

Notes
1. Four relationships involving either the absorption or emission of
radiant heat energy are as follows. 
First, Stefan-Boltzman's Law: the energy radiated from a black body
is proportional to the fourth power of the body's absolute temperature 
(T); i.e.,

Second, Wien's Law: the wavelength carrying the maximum energy is 
inversely proportional to the body's absolute temperature (T); i.e., 

Third: the temperature rise of a black-bulb thermometer, heated by a 
standard 100 W light bulb for 180 s, is proportional to the inverse-
square of the distance (D; within the range of 0.06 - 0.14 m); i.e.,

And fourth: the temperature rise of a yellow-, green-, or purple-bulb
thermometer, heated at a distance of 0.060 m by a standard 100 W 
light bulb, is roughly proportional to the fourth root of time (t; 
within the range 0 - 240 s); i.e., 

2. Apart from your notes and standard textbooks, sources of scientific
knowledge include encyclopaedias in libraries, on CD-ROMs, and on the
Web; it is good practice to include a bibliography in your write-up.

3. You are provided with clear-film, LDRs, light bulbs, paints, metals, 
mirrors, photo-paper, thermometers, and thermistors; in addition, you
will need to use - within reason - other suitable apparatus.

4. The proposed plans of your investigation should be presented in
detail; these plans may be modified as the investigation proceeds.

Dr. R. Peters                  Next                      Contents' List