A current carrying closed loop in the form of a right angle isosceles triangle $A B C$ is placed in a…

A current carrying closed loop in the form of a right angle isosceles triangle $A B C$ is placed in a uniform magnetic field acting along $A B$. If the magnetic force on the $\operatorname{arm} B C$ is $\mathbf{F}$, the force on the arm $A C$ is
  1. $-\mathbf{F}$
  2. $\mathbf{F}$
  3. $\sqrt{2} \mathbf{F}$
  4. $-\sqrt{2} \mathbf{F}$

Solution

$\begin{gathered} \overrightarrow{\mathbf{F}}_{A B}=0 \\ \overrightarrow{\mathbf{F}}_{A B}+\overrightarrow{\mathbf{F}}_{B C}+\overrightarrow{\mathbf{F}}_{C A}=0 \\ \overrightarrow{\mathbf{F}}_{B C}+\overrightarrow{\mathbf{F}}_{C A}=0 \\ \overrightarrow{\mathbf{F}}_{C A}=-\overrightarrow{\mathbf{F}}_{B C}=-\overrightarrow{\mathbf{F}} \end{gathered}$

Asked in: NEET 2011 (Screening)

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