If the concept is still too abstract, another example is a rechargeable battery. Two different metals are in the same solution and they build up different electrochemical potentials; this means there is a voltage difference between them. This is because positive parts of the metal go into the surrounding solution. After connecting the two metals, a current will flow. Electrons will travel from the less noble metal to the more noble metal. The less noble metal will then release even more positive particles into the solution. This causes it to corrode, and the noble metal picks positive particles up again. This is exactly what happens in nature, but this time the current flows through a cable and the current powers a device, like a lightbulb. When the battery is recharged, this process is reversed. A current is applied to move electrons from the noble metal to the less noble metal. This is similar to what happens during electrolysis. A current or voltage is used to initiate a reaction. Applying a voltage that triggers a reaction and measuring a current allows one to learn at which potential a reaction is triggered, how fast it is happening, or how much of the reacting species is present.