The torque that a uniform magnetic field exerts on a flat (planar) coil is given by T = NBIAsin 0, where N is the number of turns of wire in the coil, B the magnitude of the magnetic field, I the current flowir in the coil, A the area enclosed by the coil, and 0 the angle between the line perpendicular to the plane of th coil and the direction of the magnetic field. The expression given above was derived for a rectangular coil bu it is valid for any planar coil. The area enclosed by the coil can be square, rectangular, circular, ellipsoidal (as in this problem), or any other two-dimensional shape. In the situation shown in the figure redrawn below, the magnetic field is parallel to the plane of the coil. 40.0 cm В |-30.0 cm-| d Thus, the angle between the magnetic field and the line perpendicular to the plane of the coil is 0 = 90.0°. With a semimajor axis of a = (0.400 m)/2 and a semiminor axis of b = (0.300 m)/2, the area enclosed by th coil is A = nab = Tt m2, and the magnitude of the torque exerted on the coil is T = NBIAsin 0 ]a m2)sin 90.0° = 8 х 10-4 x 10¬4 N · m. %3D

University Physics Volume 2
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Chapter11: Magnetic Forces And Fields
Section: Chapter Questions
Problem 85AP: Acircularcoiofwireofradius5.Ocmhas2Otums and carries a current of 2.0 A. The coil lies in a magnetic...
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The torque that a uniform magnetic field exerts on a flat (planar) coil is given by
T = NBIAsin 0,
where N is the number of turns of wire in the coil, B the magnitude of the magnetic field, I the current flowing
in the coil, A the area enclosed by the coil, and 0 the angle between the line perpendicular to the plane of the
coil and the direction of the magnetic field. The expression given above was derived for a rectangular coil but
it is valid for any planar coil. The area enclosed by the coil can be square, rectangular, circular, ellipsoidal (as
in this problem), or any other two-dimensional shape.
In the situation shown in the figure redrawn below, the magnetic field is parallel to the plane of the coil.
40.0 cm
B
|-30.0 cm→|
d
Thus, the angle between the magnetic field and the line perpendicular to the plane of the coil is 0 = 90.0°.
With a semimajor axis of a =
coil is
(0.400 m)/2 and a semiminor axis of b = (0.300 m)/2, the area enclosed by the
A = nab =
Tt m2,
and the magnitude of the torque exerted on the coil is
T = NBIAsin 0
| × 10-4 T)( [
m2 )sin 90.0°
= 8
x 10-4 N ·m.
Note that by the right-hand rule, the magnetic force exerted on the left side of the coil is directed out of the
page while the force exerted on the right side is into the page. Thus, an observer looking from c toward d
along the dashed line shown in the diagram sees the coil rotate counterclockwise.
Transcribed Image Text:The torque that a uniform magnetic field exerts on a flat (planar) coil is given by T = NBIAsin 0, where N is the number of turns of wire in the coil, B the magnitude of the magnetic field, I the current flowing in the coil, A the area enclosed by the coil, and 0 the angle between the line perpendicular to the plane of the coil and the direction of the magnetic field. The expression given above was derived for a rectangular coil but it is valid for any planar coil. The area enclosed by the coil can be square, rectangular, circular, ellipsoidal (as in this problem), or any other two-dimensional shape. In the situation shown in the figure redrawn below, the magnetic field is parallel to the plane of the coil. 40.0 cm B |-30.0 cm→| d Thus, the angle between the magnetic field and the line perpendicular to the plane of the coil is 0 = 90.0°. With a semimajor axis of a = coil is (0.400 m)/2 and a semiminor axis of b = (0.300 m)/2, the area enclosed by the A = nab = Tt m2, and the magnitude of the torque exerted on the coil is T = NBIAsin 0 | × 10-4 T)( [ m2 )sin 90.0° = 8 x 10-4 N ·m. Note that by the right-hand rule, the magnetic force exerted on the left side of the coil is directed out of the page while the force exerted on the right side is into the page. Thus, an observer looking from c toward d along the dashed line shown in the diagram sees the coil rotate counterclockwise.
Tutorial Exercise
An eight-turn coil encloses an elliptical area having a major axis of 40.0 cm and a minor axis of 30.0 cm (see
figure). The coil lies in the plane of the page and carries a clockwise current of 6.17 A. If the coil is in a
uniform magnetic field of 1.92 x 10-4 T directed toward the left of the page, what is the magnitude of the
torque on the coil? Hint: The area of an ellipse is A = nab, where a and b are, respectively, the semimajor and
semiminor axes of the ellipse.
B
40.0 cm
- 30.0 cm-|
Transcribed Image Text:Tutorial Exercise An eight-turn coil encloses an elliptical area having a major axis of 40.0 cm and a minor axis of 30.0 cm (see figure). The coil lies in the plane of the page and carries a clockwise current of 6.17 A. If the coil is in a uniform magnetic field of 1.92 x 10-4 T directed toward the left of the page, what is the magnitude of the torque on the coil? Hint: The area of an ellipse is A = nab, where a and b are, respectively, the semimajor and semiminor axes of the ellipse. B 40.0 cm - 30.0 cm-|
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