All electromagnetic waves in a vacuum have the same

1. Analyze the question The question asks which property is the same for all electromagnetic waves (radio waves, microwaves, infrared, visible light, UV, X-rays, gamma rays) when they travel in a vacuum.

2. Explain the concept Electromagnetic waves are produced by oscillating electric and magnetic fields. They differ in wavelength and frequency, but they all travel at the same speed in a vacuum. This speed is the speed of light:

c ≈ 3.0 × 10⁸ m/s

The wave equation links these quantities:

c = fλ

Since c is fixed in a vacuum, a wave with a higher frequency must have a shorter wavelength, and the reverse is also true.

3. Go through the options

• A. Wavelength: This is wrong. Radio waves can be metres or kilometres long, while gamma rays are smaller than an atom.
• B. Frequency: This is wrong. Frequency varies across the spectrum, from low for radio waves to very high for gamma rays.
• C. Speed: This is correct. All of them travel at 3.0 × 10⁸ m/s in a vacuum.
• D. Amplitude: This is wrong. Amplitude depends on the source and the energy of the wave, so it can be anything.

4. Answer The correct option is C. speed.

5. Exam tip Remember this: "In a vacuum, all EM waves have the same speed, c." Then use c = fλ to reason about the rest. If frequency goes up, wavelength goes down, and speed stays constant. WAEC often asks this question in different forms, such as "What is common to all EM waves?" The answer is usually that they travel at the same speed in a vacuum, and that they are transverse waves.