The magnetic field at the center of a circular coil of radius r is π times that due to a long straight wire at a distance r from it, for equal currents. Figure here shows three cases: in all cases the circular part has radius r and straight ones are infinitely long. For same current the B field at the center P in cases 1, 2, 3 have the ratio
A
B
C
D
Text Solution
Verified by ExpertsThe correct answer is:
A
In figure 
In fig. (2), No field at center due to straight part.
In fig. (3), field at P due to upper straight part 
∴ Total field a P
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