The diagram represents a satellite communication link between two points on Earth. The
distances between the transmitting station, the satellite and the receiving station are shown.
The frequency of the waves used for the link can be taken as 1.5 × 10¹⁰ Hz, and the speed of
light as 3.0 × 10⁸ m / s.
What type of wave is used in such a link, and what is the time delay between a signal being
transmitted and then being received at the receiving station?

Answer:

15) D

Let us start by calculating the time delay first.

Total distance = 45000 + 45000 = 90000 Km

Speed = 3.0 ×108 m/s = 3.0 ×105 km/s

Time = (90000) ÷ (3.0 ×105 km/s) = 0.3 s

We can rule out options A, B, C, E, F and G. We are left with options D and H.

We know the formula = 

c = ƒ x λ 

λ = c/ƒ = [(3.0 × 108) ÷(1.5 × 1010 Hz)] = 0.02 m 

Since the number obtained for wavelength is larger than wavelength of the visible light, the waves must be microwaves.

Hence the answer is: D