Question

What is the equivalent radius of the earth when the ray appears to be a straight line over a flat earth surface?

(a) 0

(b) Infinity

(c) Actual radius

(d) 4/3 times actual radius

The question was posed to me at a job interview.

My enquiry is from Radio Wave Propagation in portion Radio Wave Propagation of Antennas

Answer 1

The correct option is (b) Infinity

Explanation: When the ray appears to be a straight line over a flat earth surface horizontally, its refractive index is not changing with respect to height. \(\frac{dM}{dh}=0\)

Effective radius is k times the actual radius and \(k=0.048/\frac{dM}{dh}=∞\)