A flat circular coil of radius 3.6cm and 40 turns lie on atabletop. At time t=0

Question

A flat circular coil of radius 3.6cm and 40 turns lie on atabletop. At time t=0 an external magnetic fieldperpandicular to the plane of the coil has a valuc of B=0.32 T andis decreasing linearly with time. At t=0, the induced emf is65 mV. How long will it take for the magnetic field to reach0 value? What is the direction of the induced current as the fielddecreases (CW or CCW)? A flat circular coil of radius 3.6cm and 40 turns lie on atabletop. At time t=0 an external magnetic fieldperpandicular to the plane of the coil has a valuc of B=0.32 T andis decreasing linearly with time. At t=0, the induced emf is65 mV. How long will it take for the magnetic field to reach0 value? What is the direction of the induced current as the fielddecreases (CW or CCW)?

Explanation / Answer

Radius (r) of the circular coil = 3.6 cm = 0.036 m Then area (A) of the circular coil is               A = r2                  = (0.036m)2                  = 0.00407m2 Induced emf () = 65 mV = 65.0*10-3V Change in the magnetic field is dB = 0.32 T Number of turns in the coil = 40 Then we know the formula                     = NA(dB / dt)                  dt = NA(dB) /                      = (40)(0.00407m2)(0.32T) / (65.0*10-3V)                       =0.801 s

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