Q34 of 92 Page 249

An electron makes 3 × 105 revolutions per second in a circle of radius 0.5 angstrom. Find the magnetic field B at the centre of the circle.

no of revolutions = 3 × 105


radius = 0.5 angstrom = 5×10−11 m


Thus, the magnetic field at the centre due to the current in the loop is given by


We know that,



Here n=1,


I= =


and r= 5×10−11 m


Hence,




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A circular loop of one turn carries a current of 5.00 A. If the magnetic field B at the centre is 0.200 mT, find the radius of the loop.

 33

A current carrying circular coil of 100 turns and radius 5.0 cm produces a magnetic field of 6.0 × 10–3 T at its centre. Find the value of the current.

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A conducting circular loop of radius a is connected to two long, straight wires. The straight wires carry a current i as shown in figure. Find the magnetic field B at the centre of the loop.


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Two circular coils of radii 5.0 cm and 10 cm carry equal currents of 2.0 A. The coils have 50 and 100 turns respectively and are placed in such a way that their planes as well as the centers coincide. Find the magnitude of the magnetic field B at the common centre of the coils if the currents in the coils are (a) in the same sense (b) in the opposite sense.