Question

The ammeter shown in figure consists of a $480\Omega$ coil connected in parallel to a $20\Omega$ shunt. Find the reading of the ammeter.

• A. $0.125A$
• B. $0.225A$
• C. $0.335A$
• D. $0.445A$

Answer 1

The correct option is A $0.125A$

The ammeter coil of resistance $480\Omega$ and shunt of $20\Omega$ are connected in parallel, therefore equivalent resistance

$R^{\prime }=\frac{480\times 20}{480+20}=19.2\Omega$

Now, resistance of $140.8\Omega$ and $19.2\Omega$ are in series, hence total resistance in the circuit,

$R=R^{\prime }+19.2=140.8+19.2=160\Omega$

Therefore, current in the circuit (reading by ammeter),

$I=\frac{E}{R}=\frac{20}{160}=0.125A$