Question T3B11
From subelement T3 - T3B
What is the approximate velocity of a radio wave in free space?
Why is this correct?
Radio waves are electromagnetic waves that travel at the speed of light in free space, which is approximately 300,000,000 meters per second. This is a fundamental constant of physics. Choice A (150,000 m/s) is far too slow, while choices C and D use miles per hour instead of the standard meters per second units, making them incorrect even though C has the right numerical value.
Memory tip
Remember that all electromagnetic waves—radio, light, X-rays—travel at the same speed in vacuum. The key pattern: when you see velocity questions about radio waves in free space, think 'speed of light' and look for the answer in meters per second, not miles per hour.
Learn more
This velocity constant enables all radio frequency calculations in amateur radio practice. When you calculate antenna dimensions using the formula λ = 300/f (wavelength equals 300 divided by frequency in MHz), that 300 comes from this speed of light value. Understanding this relationship helps with antenna modeling, propagation predictions, and timing calculations for digital emission standards and repeater coordination.
Think about it
Why do you think radio waves maintain this constant velocity regardless of their frequency, while sound waves change speed in different materials?