Question

An ideal ammeter A is connected as shown in the diagram. Ammeter reading is:

• A. $\frac{2E}{r}$
• B. $\frac{5E}{r}$
• C. $\frac{E}{r}$
• D. $\frac{E}{2r}$

Answer 1

Answer: (A)

$\frac{2E}{r}$

We know, the equivalent of $N$ resistors of resistors connected in parallel is $\frac{R}{N}$.
As the ammeter is ideal, we can assume it to be a conducting wire for calculation purposes.
The equivalent thus found is $\frac{r}{5}$.
The current drawn from battery is then,$\frac{E}{\frac{r}{5}}=\frac{5E}{r}$.
This current now must get equally distributed among all the resistors, hence current through each resistor is $\frac{E}{r}$.
Combined current through bottom two resistors is then $\frac{2E}{r}$, which will be the reading of Ammeter.