Question

If the ammeter A shows a zero reading in the circuit shown above, the value of resistance R is

• A. $500\Omega$
• B. $125\Omega$
• C. $100\Omega$
• D. $41.5\Omega$
• E. $4\Omega$

Answer 1

The correct option is B $125\Omega$

If ammeter show zeroreading that means no current is passing through ammeter $A$ and resistor $R$ (because of $2V$ battery),
Applying Kirchoff voltage law in Ist loop assuming current in $1st$ loop to be $i$,
$500i+iR=10$ ....eqn 1
Applying Kirchoff voltage law in $2nd$ loop,
$iR=2$ ...... eqn 2

Solving both eqn we get $i=1.6\times {10}^{-2}A$ and $R=125ohm$