To understand the origins of both of Kirchhoff's rules and how to use them to solve a circuit problem. This problem introduces Kirchhoff's two rules for circuits: Kirchhoff's loop rule: The sum of the voltage changes across the circuit elements forming any closed loop is

Helium is trapped in earth's crust mainly as a by-product of decay chain cycle of radioactive isotopes including uranium-238, uranium-235 and thorium-232. these radioactive isotopes continually decay  to  emit radioactive particles including alpha, beta and gamma  rays. when an alpha particle, each containing two protons and two neutrons, collide with two electrons, they form a helium atom. since earth's crust contains these radioactive particles, therefore much of helium is produced within earth's crust and gets trapped in it.