Question

how does current become weak

Answer 1

 particle physics, the weak interaction (the weak force or weak nuclear force) is the mechanism of interaction between subatomic particles that causes radioactive decay and thus plays an essential role in nuclear fission. The theory of the weak interaction is sometimes called quantum flavordynamics (QFD), in analogy with the terms quantum chromodynamics (QCD) dealing with the strong interaction and quantum electrodynamics(QED) dealing with the electromagnetic force. However, the term QFD is rarely used because the weak force is best understood in terms of electroweak theory (EWT).[1]

The weak interaction takes place only at very small, sub-atomic distances, less than the diameter of a proton. It is one of the four known fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation.

Answer 2

The current becomes weak by external factors such as weak battery, too many bulbs in one circuit or material or metal of which wire is made.
Regards—HarshAgrawal