EM 1110-2-2907
1 October 2003
gree sign). The Kelvin scale has the same temperature intervals as the Celsius scale, so
conversion between the two scales is simply a matter of adding or subtracting 273 (Table
2-1). Because all objects with temperatures above, or higher than, zero Kelvin emit elec-
tromagnetic radiation, it is possible to collect, measure, and distinguish energy emitted
from adjacent objects.
Table 2-1
Different scales used to measure object temperature. Conversion formulas are listed
below.
Fahrenheit (oF)
Celsius (oC)
Object
Kelvin (K)
Absolute Zero
459.7
273.2
0.0
Frozen Water
32.0
0.0
273.16
Boiling Water
212.0
100.0
373.16
Sun
9981.0
5527.0
5800.0
Earth
46.4
8.0
281.0
Human body
98.6
37.0
310.0
Conversion Formulas:
Celsius to Fahrenheit: F = (1.8 x C) + 32
Fahrenheit to Celsius: C = (F- 32)/1.8
Celsius to Kelvin: K = C + 273
Fahrenheit to Kelvin: K = [(F- 32)/1.8] + 273
Figure 2-3. Propagation of the electromagnetic and magnetic field. Waves vibrate
perpendicular to the direction of motion; electric and magnetic fields are at right
angle to each other. These fields travel at the speed of light.
e. Nature of Electromagnetic Waves. Electromagnetic energy travels along the path
of a sinusoidal wave (Figure 2-3). This wave of energy moves at the speed of light (3.00
8
10 m/s). All emitted and reflected energy travels at this rate, including light. Electro-
magnetic energy has two components, the electric and magnetic fields. This energy is
defined by its wavelength (λ) and frequency (ν); see below for units. These fields are in-
phase, perpendicular to one another, and oscillate normal to their direction of propagation
(Figure 2-3). Familiar forms of radiant energy include X-rays, ultraviolet rays, visible
2-4
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