2. Questions Bank
  3. JEE Main & Advanced
  4. Physics
  5. Magnetism

JEE Main & Advanced Physics Magnetism Question Bank Critical Thinking

  • question_answer
    A small coil C with N = 200 turns is mounted on one end of a balance beam and introduced between the poles of an electromagnet as shown in figure. The cross sectional area of coil is A= 1.0 cm2, length of arm OA of the balance beam is \[l=30\,cm.\] When there is no current in the coil the balance is in equilibrium. On passing a current I = 22 mA through the coil the equilibrium is restored by putting the additional counter weight of mass \[\Delta m=60\,mg\] on the balance pan. Find the magnetic induction at the spot where coil is located.

    A)            0.4 T                                         

    B)            0.3 T

    C)            0.2 T                                         

    D)            0.1 T

    Correct Answer: A

    Solution :

                       On passing current through the coil, it acts as a magnetic dipole. Torque acting on magnetic dipole is counter balanced by the moment of additional weight about position O. Torque acting on a magnetic dipole            \[\tau =MB\sin \theta =(NiA)B\sin {{90}^{o}}=NiAB\].                    Again \[\tau =Force\times Lever\ arm\ =\Delta mg\times l\]                    \[\Rightarrow NiAB=\Delta mgl\]            \[\Rightarrow B=\frac{\Delta mgl}{NiA}=\frac{60\times {{10}^{-3}}\times 9.8\times 30\times {{10}^{-2}}}{200\times 22\times {{10}^{-3}}\times 1\times {{10}^{-4}}}\]= 0.4 T


You need to login to perform this action.
You will be redirected in 3 sec spinner