All parts of the electromagnetic spectrum travel at a speed of 3 × 108 m/s when traveling through no medium. a "vacuum” means that there is no medium, such as a tube without any air in it. therefore, 3 × 108 m/s is said to be the speed of light in a vacuum. if an electromagnetic wave’s frequency doubles in a vacuum, what are the other effects on the wave? wavelength doubles and speed doubles. wavelength doubles and speed stays the same. wavelength divides in half and speed doubles. wavelength divides in half and speed stays the same