The circuit diagram below, contains a combination of four resistors, with resistance R, two
ammeters, A1 and A2, a cell with EMF of 12 V and switch, S. S is open and the readings on
A1 and A2 are taken.
S is now closed and the readings taken again. The following is observed:
- Before closing the switch S, no current flows through the circuit, so the readings on both ammeter A1 and A2 are zero.
- After closing the switch S, current starts flowing through the circuit. The current will be the same at all points in a series circuit.
- Since resistors R1, R2, R3, and R4 are in series, the total resistance in the circuit is equal to the sum of their resistances, which is 4R.
- According to Ohm's Law (V = IR), the current (I) will be equal to the voltage (V) divided by the total resistance (4R), which is 12V / 4R = 3V/R.
Therefore, after closing the switch S, the readings on both ammeter A1 and A2 will be 3V/R.