WS/EO1 : Electro-Optics Theory

Question 1

Define Electro Optics (EO).

Answer 1

Electro Optics is the generation, modulation, detection and
measurement, or display of optical radiation by electrical means.

Question 2

Describe Infrared radiation.

Answer 2

Infrared energy is produced by heat but should not be confused as heat.

Question 3

Define the Optical spectrum.

Answer 3

Extreme Ultraviolet (UV) through the visible to the extreme Infrared
(IR)

Question 4

Define Radiant Exitance

Answer 4

Radiant power per unit area emitted from a surface. (Unit of
measure = Wm-2) (W=Watts)

Question 5

Define Irradiance

Answer 5

Radiant power per unit area incident upon a surface. (Unit of
measure = Wm-2 or commonly Wcm-2)

Question 6

Define Radiant Power

Answer 6

Rate of transfer of radiant energy (W)

Question 7

Define Absolute Temperature

Answer 7

Refers to the temperature as measured on a scale determined
by certain general thermo-dynamic principles, and reckoned
from the absolute zero or 0°Kelvin.

Question 8

Define Emissivity

Answer 8

The ratio of the radiant exitance of the source to the radiant
exitance of a perfect radiator, at the same temperature
(Expressed as a decimal).

Question 9

Define Black Body Radiators

Answer 9

A black body is defined as an object, which completely absorbs all radiation incident upon it. Conversely, the radiation emitted by a black body at any given temperature is the maximum possible.
Emissivity = 1

Question 10

Define Grey Body Radiators

Answer 10

A grey body is a less than perfect absorber or emitter with an
emissivity of less than unity (1).

Question 11

Define Selective Radiators

Answer 11

A Grey body whose emissivity varies with wavelength. Selective
radiators mainly radiate over a narrow BW.

Question 12

TSTW

List the Factors Affecting Emissivity

Answer 12

• Type of material.
• Surface finish.
• Temperature.
• Wavelength.

Question 13

MOOR

Describe Optical Radiation Properties

Answer 13

• May be polarised.
• Refracts through a non-uniform body.
• Obeys the laws of Reflection, Refraction & Diffraction.
• Optical radiation is emitted by any body whose temp is greater than -273 °C (absolute zero).

Question 14

List the key Environmental Effects on IR radiation

Answer 14

The key environmental effects on IR are:
– Absorption
– Scattering
– Atmospheric Scintillation
– Background effects