Question

Calculate the equivalent resistance of the given circuit and also find the ammeter reading.

• A. $5\Omega ,1.2A$
• B. $5\Omega ,1.2A$
• C. $15\Omega ,1.8A$
• D. $45\Omega ,7.5A$

Answer 1

The correct option is A $5\Omega ,1.2A$

We can see that basically the three resistors are in parallel.

So the circuit can be redrawn as

Therefore voltage drop across each resistance is same as the provided by the battery.
The current through the ammeter is same as the current through the equivalent resistance of the circuit.
Hence, ammeter reading (A) = $\frac{V}{R_{eq}}$

Now, $\frac{1}{R_{eq}}$ = $\frac{1}{R_1}$ + $\frac{1}{R_2}$ + $\frac{1}{R_3}$
$⟹\frac{1}{R_{eq}}=\frac{1}{15\Omega }$ + $\frac{1}{15\Omega }$ +$\frac{1}{15\Omega }$

= $\frac{1}{5\Omega }$

$R_{eq}=5\Omega$

So, ammeter reading(A) = $\frac{6}{5}$ = $1.2A$