A coil of radius 20 cm is placed in an external magnetic field of strength 0.20

Question

A coil of radius 20 cm is placed in an external magnetic field of strength 0.20 T such that the plane of the coil is perpendicular to the field. The coil is pulled out of the field in a time of 0.30 s. Find the average induced emf during this time. A flexible circular loop has a radius of 12 cm and is in a uniform magnetic field of strength of 0.15 T such that the plane of the loop makes an angle of 30 degree with the field. The loop is grasped at two opposite points along a diameter and stretched, without altering its orientation, until it closes. If it takes 0.20 s to close the loop, find the magnitude of the average induced emf in it during this time. Over a region where the vertical component of the Earth's magnetic field is 40 mu T directed downward, a 5.0 m length of wire is held along an east-west direction and moved horizontally to the north with a speed of 10 m/s. Calculate the potential difference between the ends of the wire and determine which end is positive.

Explanation / Answer

A=pi*r^2 = pi*(0.2)^2 = 0.126 m^2

flux = B*A = 0.2*0.126 = 0.0251

emf= - (flux change)/(time interval) = - (0.0251)/(0.3) = - 0.0838 v

but the average during time it was pulled out (0.3s) is

emf/t= -0.279 V/s

2. EMF = /t = BA/t = (0.15)(0.12)²*cos(30) / (0.12) = 48.97 mV

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