RAJASTHAN ­ PET Rajasthan PET Solved Paper-2003

  • question_answer
    In the following figure, a coil of radius 2 cm is shown along with a coil of radius 7 cm present at   its centre. Each coil has 100 round and big coil has 5 A current. What should be the current in small coil so that total magnetic field at centre is 2 mT?

    A)  1.44 A            

    B)  0.793 A

    C)  2.88 A            

    D)  3.4 A

    Correct Answer: B

    Solution :

     Suppose the magnetic fields due to big and small coils are By and B^ respectively. \[\therefore \] \[{{B}_{1}}=\frac{{{\mu }_{0}}NI}{2{{a}_{1}}}\] Or \[{{B}_{1}}=\frac{4\pi \times {{10}^{-7}}\times 100\times 5}{2\times 0.07}\] Or \[{{B}_{1}}=4.49\,mT\] \[{{B}_{2}}=\frac{{{\mu }_{0}}NI}{2{{a}_{2}}}=\frac{4\pi \times {{10}^{-7}}\times 100\times {{I}_{2}}}{2\times 0.02}\] Again,    \[B={{B}_{1}}-{{B}_{2}}=2\] \[{{B}_{2}}={{B}_{1}}-B\] \[=4.49-2=2.49\text{ }mT\] Now, \[{{I}_{2}}=\frac{2.49\times {{10}^{-3}}\times 2\times 0.02}{4\pi \times {{10}^{-7}}\times 100}\] \[=0.793A\]


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