Module 3_2 Quiz

1. Which one of the following must be present for a duct to exist?

a) An ocean surface below
b) A negative M gradient (i.e.a vertical region where M decreases with eelvation)
c) A positive temperature gradient (i.e. temperature increase with elevation)
d) Light winds
e) Feathers, webbed feet and a beak

2. What is the difference between a surface duct and a surface-based duct?

a) Nothing. They are the same thing.
b) A surface duct extends to the surface while a surface-based duct does not.
c) The trapping layer (negative M gradient) extends to the surface for a surface duct but not for a surface-based duct.
d) For a surface duct, the minimum M is lower than the surface M value, while for a surface-based duct the surface has the lowest M value anywhere.
e) A. Surface ducts build their nests on the surface while surface-based ducts feed at the surface but build nests in trees.

3. Consider a surface-based duct. What happens to the propagation when the duct becomes stronger, i.e. the difference in M value from the surface to duct top becomes greater?

a) The skip zones become larger.
b) There are more skip zones.
c) Both a and b are correct.
d) None of the above are correct.
e) The duct can quack louder.

4. What is the relation between duct thickness and transmission frequency?

a) There is no relationship; all frequencies are trapped within a duct.
b) Thicker ducts can trap EM radiation at higher frequencies.
c) Thicker ducts can trap EM radiation at lower frequencies.
Thicker ducts can trap EM radiation at both higher and lower frequencies.
Thicker ducts can survive in colder climates.