The one-way propagation delay for a single bit of information (travelling at the speed of light i.e., $$3 \times 10^8$$​ meters per second) over a fiber optic cable from point A to point B, 12000 kilometers apart would be:

Correct option is D

The one-way propagation delay is the time required for a bit to travel from point A to point B. We use:
​$$\text{Propagation Delay}=\frac{\text{Distance}}{\text{Propagation Speed}}$$​​
Step 1: Convert distance into meters
Given:
12000 km
Since:
1 km = 1000 m
Therefore:
​$$12000\times1000=12,000,000\text{ m}\\=1.2\times10^7\text{ m}$$​​
Step 2: Calculate the delay
Speed of light:
​$$3\times10^8\text{ m/s}$$​​
Therefore:
​$$T=\frac{1.2\times10^7}{3\times10^8}$$​​
​$$T=0.4\times10^{-1}$$​​
T = 0.04 s
Step 3: Convert seconds to milliseconds
1 s = 1000 ms
Therefore:
​$$0.04\times1000=40\text{ ms}$$​​
Hence:
Propagation Delay = 40 ms
Information Booster
1. Propagation delay is:
​$$\boxed{T_p=\frac{d}{v}}$$​​
2. Distance:
​$$12000\text{ km}=1.2\times10^7\text{ m}$$​​
3. Speed:
​$$v=3\times10^8\text{ m/s}$$​​
4. Thus:
​$$T_p=0.04\text{ s}=40\text{ ms}$$​​
5. This is one-way propagation delay. A round-trip delay would be:
​$$2\times40=80\text{ ms}$$​​