Exercises
What physical quantity is the same for X-rays of wavelength 10⁻¹⁰ m, red light of wavelength 6800 Å and radiowaves of wavelength 500 m?
X-rays (λ = 10⁻¹⁰ m), red light (λ = 6800 Å = 6.8 × 10⁻⁷ m), and radiowaves (λ = 500 m) are all electromagnetic waves — members of the electromagnetic spectrum.
Despite having vastly different wavelengths and frequencies, all electromagnetic waves travel through vacuum with the same speed:
c = 3 × 10⁸ m/s
Verification of frequencies:
X-rays: f = c/λ = 3 × 10⁸ / 10⁻¹⁰ = 3 × 10¹⁸ Hz
Red light: f = 3 × 10⁸ / 6.8 × 10⁻⁷ = 4.4 × 10¹⁴ Hz
Radiowaves: f = 3 × 10⁸ / 500 = 6 × 10⁵ Hz
The frequencies differ enormously, but the speed in vacuum is the same for all.
Answer: The speed in vacuum: c = 3 × 10⁸ m/s is the same for all three — X-rays, red light, and radiowaves are all electromagnetic waves traveling at the same speed in vacuum.