The Invariance of the Speed of Light
The Speed of Light
- In a vacuum, light travels at a speed of 3.0 × 108 ms-1, which is given the symbol c
- When travelling through different materials, the speed of light may reduce but it can never exceed c
What does invariance mean?
- The invariance of light means that when in a vacuum, the speed of light is always 3.0 × 108 ms-1 for every observer
- Light still travels at this speed even when emitted from a moving object
Diagram demonstrating the invariance of the speed of light
Light does not travel at 3.0 × 108 ms-1 plus the speed of the person running, to all observers it just travels at 3.0 × 108 ms-1
- This concept only applies to light, as it is the only thing capable of traveling at the speed of light
- The invariance of the speed of light has some very surprising consequences, which will be explored in the following revision notes...
Exam Tip
The invariance of the speed of light may feel counter-intuitive at first, but remember that nothing can travel faster than the speed of light, so if you ever end up with an answer for velocity bigger than 3.0 × 108 ms-1, something has gone wrong!
