Two converging lenses with the focal lengths f 1 = 0.2 m and f2 = 0.4 m are positioned at a distance f1 + f2 to each other. such arrangements are called "beam expanders" and are often used in laser technology
a) what is the expansion ratio w2 / w1?
one of the two converging lenses is now to be replaced by a diverging lens, with the same expansion ratio w2 / w1 to be achieved.
b) which of the two lenses is that and what is the focal length of the dissipation lens?
c) what is the distance of the lenses now?

Answer///air resistance,drag;

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current