How can Electricity travel at the speed of light?

Question

If electricity is the flow of electrons, how come it can flow at the speed of light? Shouldn't how fast it moves be limited to a speed lower than the speed of light because it has mass?

Answer 1

Electricity does not move at the speed of light. In a conductor the individual electron drift velocity is often surprisingly low, while the signals and energy are transmitted far faster. Electromagnetic waves move near the speed of light... but if the medium has an index of refraction $n$ the speed will be $c/n$. Similarly in a cable the capacitance and inductance produce a signal speed that is lower than in free space.

Answer 2

What happens is exactly the same as what happens in a garden hose that contains water heated by the sun. When you open the valve, water comes out immediately. It takes a while for cold water to come out of the open end. The start of the joint movement of the water molecules when the tap is opened is incredibly fast, but the individual molecules have a much lower flow velocity.

Exactly the same happens with an electric current. The information about changes in the current reaches the other end of the line almost at the speed of light, whereas the individual electrons move forward rather very sluggishly.

Answer 3

Consider a Newton's cradle. You lift up and release the ball at one end. Just before it strikes the next ball, it has a certain velocity $v$, which depends on how for you initially raised the ball. Very soon after the collision, the ball at the other end starts to move. The "motion" is propagated from the ball on one end to the one at the other at about the speed of sound $v_s$ in the material the balls are made of, which is much greater than $v$. This is in spite of the fact that at no point during this process is any one ball moving faster than $v$: there is just not enough energy in the system for this to happen.

This is largely analogous to the propagation of electric signals in wires. The electron drift velocity is like $v$, and the speed of light is like $v_s$.