MCQ
The figure shows a conducting loop $ABCDA$ placed in a uniform magnetic field perpendicular to its plane. The part $ABC$ is the $(3/4)^{th}$ portion of the square of side length $l$ . The part $ADC$ is a circular arc of radius $R$ . The points $A$ and $C$ are connected to a battery which supply a current $I$ to the circuit. The magnetic force on the loop due to the field $B$ is
  • A
    Zero
  • $BI l$
  • C
    $2BIR$
  • D
    $\frac{{BI/R}}{{l + R}}$

Answer

Correct option: B.
$BI l$
b
Introducing two equal and opposite current $I_{1}$ and $a l s o I_{2}$ between $A \& C$

Force on $ABCA$ closed loop zero

Force on $ADCA$ closed loop zero

Force on extra $I_{1} \& I_{2}$

$F=\left(I_{1}+L_{2}\right) l B=I / B$

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