Parallel Wires: Two long, parallel wires carry currents of different magnitudes. If the current in one of the wires is doubled and the current in the other wire is halved, what happens to the magnitude of the magnetic force that each wire exerts on the other?

Explanation:

Given force between 2 currents carrying

wires = F₀

Magnetic force between the2 wires =F₀= (μ₀/4π) x ( 2 (μ₀/4π) x ( 2I₁I₂ / μ) x L

where I₁=Current in wire 1

           I₂= Current in wire 2

           L= Length of the wire

when one current is doubled and the other is halved

I₁= 2 I₁

I₂=    I₂/2

F₀ = (μ₀/4π) x ( 2× (2I₁) (I₂/2) / μ) x L

connect the batteries in series and hope

the answer is 12 as i may remember

: )