It's a circuit in which the current flows through all the components without branching. (T)
Req= R1+R2+R3+R4+.............Rn
Parallel circuit:
It's a circuit in which the current flows through two or more branches.
2R=>Req=R1*R2/R1+R2
3 or more R=>Req=(1/(1/R1)+(1/R2)+(1/R3)+........(1/Rn))
In a parallel circuit: It=I1+I2+I3...In
