In the diagram below, a battery with an emf of 12 V and an internal resistance of 1 Ω, is
connected to three resistors with resistance R, 2R and R. A voltmeter V is connected across the
battery. The ammeter A has a negligible resistance
1) S1 and S2 are now closed and a current of 2,4 A is registered on A.
4.1 Calculate the total resistance of the external circuit in terms of R.
2 Calculate the value of R
3 Calculate the reading of V
S1 is now opened and the readings of A and V taken. Say what will happen to each of the
readings. Just write down DECREASE, INCREASE or SAME.
1) Total resistance of the external circuit in terms of R can be calculated as follows:
Total resistance = R + 2R + R = 4R
2) To calculate the value of R, we know that the total resistance is 4R and the total current is 2.4 A. Using Ohm's Law (V = IR), we can calculate the total voltage as follows:
12 V = 2.4 A * 4R
12 V = 9.6 R
R = 1.25 Ω
3) To calculate the reading of V, we know that the voltage drop across the internal resistance is given by:
V_internal = I_internal * R_internal
V_internal = 2.4 A * 1 Ω
V_internal = 2.4 V
So, the reading of V will be the EMF of the battery minus the voltage drop across the internal resistance:
V = 12 V - 2.4 V
V = 9.6 V
4) When S1 is opened, the current in the circuit will DECREASE and the voltage reading will INCREASE.