6. A loop of a wire has the shape shown in the drawing. The top part of the wire

Question

6. A loop of a wire has the shape shown in the drawing. The top part of the wire is bent into a semicircle of radius 0.19 m. The normal to the plane of the loop is parallel to a constant magnctic field of magnitude 0.77 T. What is the magnitude of the change in the magnetic flux that passes through the loop when, starting with the position shown in the drawing, the semicircle is rotated through quarter of a revolution? Wb B (into paper) 7. A rectangular coil of sides 7.00 cm and 12.0 cm contains 145 loops and its plane is positioned perpendicular to a uniform 0.66-T magnetic field, as shown. It is quickly and uniformly pulled from the field to a region where the B-field drops abruptly to zero. It takes 0.18 s for the whole coil to reach the field-free region. How much power is dissipated in the coil if its resistance is 180 ?

Explanation / Answer

6. delta(A) = ( pi r^2)/2

change in flux = B . delta(A)

= (pi x 0.19^2 / 2)(0.77)

= 0.0437 Wb

7.induced emf = rate of change of magnetic flux

e = ( (145 x 0.07 x 0.12 x 0.66) - 0) / 0.18

e = 4.466 Volt

P = e^2 / R = 4.466^2 / 180

P = 0.111 Watt

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