Question

Choose the correct option among the following.

• A. Ammeter reading is $4\text{A}$. Current through $6\Omega$ is $2\text{A}$
• B. Ammeter reading is $2\text{A}$. Current through $6\Omega$ is $4\text{A}$
• C. Ammeter reading is $2\text{A}$. Current through $6\Omega$ is $2\text{A}$
• D. Ammeter reading is $0\text{A}$. Current through $6\Omega$ is $6\text{A}$

Answer 1

The correct option is A Ammeter reading is $4\text{A}$. Current through $6\Omega$ is $2\text{A}$

$R_{eq}=\frac{3\times 6}{3+6}+1=3\Omega$

Current through battery is,

$I_T=\frac{18}{3}$ = $6\text{A}$

So current through the ammeter,

$I_A=\left(\frac{R_T}{R}\right)\times I_T=\frac{\left(\frac{3\times 6}{3+6}\right)}{3}\times 6$

$I_A=6\times \frac{6}{9}$ = $4\text{A}$

Now, current through the $6\Omega$ resistor is,

$I_{6\Omega }=(6\text{A}-4\text{A})=2\text{A}$

Hence, option (a) is the correct answer.

Why this question ? Key concept: (1). It is a devive used to measure current and it is always connected in series with the 'element' through which current is to be measured. (2). Smaller the resistance of an ammeter more accurate will be its reading. An ammeter is said to be ideal if its resistance (r) is zero. However, as practically $r\ne 0$, ideal ammeter cannot be realised in practice.