Question

Ramya wants to measure the current flowing through the circuit shown below.

Which among the four ammeters can she use for the same? Show your calculations.

Ammeter	Minimum range	Maximum range
L	0 mA	1 m A
P	0 mA	10 m A
Q	0 A	1 A
R	0 A	10 A

Answer 1

From Ohm's law, we have 

V = IR 

I = V/R 

given V = 12 V and R₁ = 2 ohm, R₂ = 8 ohm and R₃ = 4 ohm 

Therefore, 

net resistance R = R₁ + (R₂ x R₃)/ (R₂ + R₃) 

= 2 + (8 x 4/8 + 4) 

= 2 + 32/12 

= 2 + 2.66 R 

= 4.66 ohm

I = 12/4.66 

I = 2.58 A

She can use ammeter S to measure the current in the circuit.