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NCERT Class XII Chapter
Moving Charges and Magnetism
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Question : 17
Total: 28
A toroid has a core (non-ferromagnetic) of inner radius 25 cm and outer radius 26 cm, around which 3500 turns of a wire are wound. If the current in the wire is 11 A, what is the magnetic field
(a) outside the toroid,
(b) inside the core of the toroid, and
(c) in the empty space surrounded by the toroid.
Solution:  

Total turns in the toroid are given 3500.
(a) outside the toroid the magnetic field is zero.
(b) Inside the core of toroid, the magnetic field will be
B = µ0nl
B = µ0
N
2πr
 I
Here r can be taken mean of inner and outer radius i.e., 25.5 cm.
so, B =
4π×10−7
2π
3500×11
25.5×10−2
 = 3 × 10−2 T
(c) Magnetic field in the empty space surrounded by the toroid is also zero.
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