Question

Figure shows a rod PQ of length 20 cm and mass 200 g suspended through a fixed point O by two threads of length 20 cm each. A magnetic field of strength 0.5 T exists in the vicinity of the wire PQ as shown in the figure. The wires connecting PQ with the battery are loose and exert no force on PQ. A current of 2 A is established when the switch S is closed. The tension in the threads is

• A. 1.25 N
• B. 2. 25 N
• C. 3. 25 N
• D. 4. 25 N

Answer 1

The correct option is A

1.25 N

In equilibrium, $2Tcos\theta =Mg+Bil\Rightarrow 2T\times cos{30}^{\circ }=0.2\times 9.8+0.5\times 2\times 0.2\Rightarrow T=1.25N$