Ham Radio General Class Practice Test

How long does it take charged particles from coronal mass ejections to affect radio-wave propagation on the Earth?

1. 28 days

2. 14 days

3. 4 to 8 minutes

4. 20 to 40 hours

The correct answer is: 20 to 40 hours

Charged particles from coronal mass ejections (CMEs) have a significant impact on radio-wave propagation on Earth, primarily because they can disturb the ionosphere. When these charged particles are ejected from the sun, they travel through space and can reach Earth in varying times based on their energy and speed. Typically, it takes about 20 to 40 hours for the electromagnetic disturbances associated with smaller CMEs to affect radio communications. This delay is due to the time it takes for the charged particles to travel the average distance from the sun to the Earth, which is approximately 93 million miles. While higher-energy solar events or flares can cause effects in much shorter times, typical CMEs will result in noticeable impacts on radio-wave propagation within this 20 to 40 hour window after they occur. The other timeframes listed do not align with the generally observed travel time of CMEs to affect radio communications. For example, while 4 to 8 minutes may pertain to the arrival time of light or radiation from solar flares, it does not reflect the actual travel time of the charged particles themselves. Understanding this timeframe is essential for operators in predicting and managing the effects of space weather on their radio communications.