question_answer

A circuit contains an ammeter, a battery of 30V and a resistance \[40.8\,\Omega \] all connected in series. If the ammeter has a coil of resistance \[480\,\Omega \] and a shunt of \[20\,\Omega ,\] then reading in the ammeter will be   [NEET (Re) 2015]

A)  0.5 A  

B)       0.25 A 

C)  2 A                 

D)       1 A

Correct Answer: A

Solution :

[a] Effective resistance of a circuit,

\[{{R}_{eff}}=40.8+\frac{480\times 20}{480+20}\]

\[=40.8+19.2=60\Omega \]

So, current flowing across ammeter,

\[I=\frac{V}{R}=\frac{30}{60}=\frac{1}{2}=0.5A\]

Hence, reading of ammeter \[=0.5\text{ }A\]