Question

The following apparatus is available in the school laboratory:

Battery	:	4.5 V
Rheostat	:	Varies battery voltage from 0 to 4.5 V
Resistors	:	1 Ω and 2 Ω
Ammeters	:	A1 of range 0 to 1 A; Least count 0.05 A
	:	A2 of range 0 to 3 A; Least count 0.1 A
Voltmeters	:	V1 of range 0 to 5 V; Least count 0.1 V
	:	V2 of range 0 to 10 V; Least count 0.5 V

The best combination of ammeter and voltmeter for finding the resultant resistance of the two given resistors connected in series would be:
(1) ammeter A₁ and voltmeter V₁
(2) ammeter A₁ and voltmeter V₁
(3) ammeter A₂ and voltmeter V₁
(4) ammeter A₂ and voltmeter V₂

Answer 1

Maximum battery voltage in the circuit = 4.5 V

The total resistance in series = $3\text{Ω}$

Maximum Current that can be flown in the circuit = $\frac{\text{Maximum Voltage}}{\text{Total resistance}}=\frac{4.5\text{V}}{3\text{Ω}}=1.5\text{A}$

For the given set up the only ammeter A₂ will be appropriate because it can measure the maximum current in the circuit, while the ammeter A₁ can only measure current up to 1 A, so it would not be useful. Also, the voltmeter V₁ would be sufficient because it can measure the maximum possible potential difference across the resistors and it has minimum least count.

Hence, the correct answer is option 3.