The adjective cumulative describes the total amount of something when it's all added together. Eating a single chocolate doughnut is fine, but the cumulative effect of eating them all day is that you'll probably feel sick. If something is cumulative, it is heaped together so it can be counted up to get a total number. The cumulative snowfall for the whole winter isn't just the amount of snow that fell in one month, but rather the number of inches that fell every month that winter to get the total, cumulative, amount.
Light has a constant speed through a given substance. For example, it always travels at a speed of approximately 3 x 10 8 metres per second in a vacuum. This is actually the speed that all electromagnetic radiation travels-not just visible light.
In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space-time, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays. Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicul