Q63 / 75 · JEE Main 2026 (05 April Shift 1) · Physics

Refer to the figure given below, current between terminals $A$ and $B$ is _____ A.
Figure

  • A
    $12.5$
  • Correct answer
    B
    $1.25$
  • C
    $7.5$
  • D
    $5$

Solution

The given circuit consists of four parallel branches connected between the left and right common vertical wires.

Let's find the equivalent electromotive force (EMF) and resistance for each branch:
For the top three active branches, each contains three $5\text{ V}$ cells and three $3\ \Omega$ resistors in series.
Equivalent EMF of each active branch, $E = 5 + 5 + 5 = 15\text{ V}$.
Equivalent resistance of each active branch, $R = 3 + 3 + 3 = 9\ \Omega$.

Since these three identical active branches are connected in parallel, we can replace them with a single equivalent voltage source:
Equivalent EMF, $E_{eq} = 15\text{ V}$ (as they are identical and in parallel).
Equivalent internal resistance, $R_{eq} = \dfrac{9}{3} = 3\ \Omega$.

The fourth (bottom) branch is connected between terminals $A$ and $B$ and acts as the load for this equivalent source. It contains three $3\ \Omega$ resistors in series.
Resistance of the branch $AB$, $R_{AB} = 3 + 3 + 3 = 9\ \Omega$.

Now, the circuit is simplified to an equivalent source of $15\text{ V}$ with internal resistance $3\ \Omega$ connected across a load of $9\ \Omega$.
The current $I$ flowing between terminals $A$ and $B$ (through the bottom branch) is given by Ohm's law:
$I = \dfrac{E_{eq}}{R_{eq} + R_{AB}}$

$I = \dfrac{15}{3 + 9} = \dfrac{15}{12}\text{ A}$

$I = 1.25\text{ A}$

Answer: $1.25$

Hence, the correct answer is option: 'B'.

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