Voltage across open circuit (very basic question)

[jjxdd]

Vs to R1 to R2 to R3 to ground

If there is an opening in the circuit between R1 and R2, why is it that when I measure the voltage between R1 and R2, it equates to the voltage source voltage? Why does the resistor not matter?

If the circuit is normal without any opening, what will I get when I measure the voltage between the resistor?, as in just the wire? I assume 0v, but why?

 

[SirAskalot]

Have you learned Kirchoffs voltage law?

If no, think of that in every circuit the sum of the voltages across resistors and switches equals the voltage soruce. Since there is no current in the circuit, ohms law dictates that U=0V across any resistor. Therfore the sum of all voltages (resistors and openings) equals the voltage source. In this case, resistor voltage equals 0V so voltage source=switch voltage.

Second question: ohms law: U=R*I, and in a short wire R≈0.