28. Magnetic Fields and Forces

Magnets and Magnetic Fields

Multiple Choice
In a typical bar magnet, where is the magnetic force (field strength) strongest?
Multiple Choice
A long straight wire carries a current of $I$ . What is the magnetic field strength at point 1, located a distance $r$ from the wire?
Multiple Choice
Which statement best describes the magnetic field of Jupiter compared to Earth's magnetic field?
Multiple Choice
Which of the following devices operates using magnetism rather than electromagnetic radiation?
Textbook Question
A 150 g ball containing 4.00 x 10⁸ excess electrons is dropped into a 125 m vertical shaft. At the bottom of the shaft, the ball suddenly enters a uniform horizontal magnetic field that has magnitude 0.250 T and direction from east to west. If air resistance is negligibly small, find the magnitude and direction of the force that this magnetic field exerts on the ball just as it enters the field.
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Textbook Question
A long copper strip is 3.0 cm wide and thick. When it carries a steady 42-A current in a 0.80-T magnetic field it produces a 6.5-μV Hall emf. Determine:
(a) the Hall field in the conductor;
(b) the drift speed of the conduction electrons;
(c) the density of free electrons in the metal.
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Textbook Question
A particle with mass $1.81 \times 10^{- 3}$ $kg$ and a charge of $1.22 \times 10^{- 8} C$ has, at a given instant, a velocity $v = (3.00 \times 10^{4} m/s) j$ . What are the magnitude and direction of the particle's acceleration produced by a uniform magnetic field $B = (1.63 T) i + (0.980 T) j$ ?
Multiple Choice
Which option best completes the following sentence? If a magnet is carefully balanced, as in a compass, the north end of the magnet points roughly toward…
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Multiple Choice
Two long parallel wires lie in the $x y$ -plane, each carrying a $5.0$ A current in opposite directions. Wire 1 lies along the $y = 3.0 cm$ line and carries a current in the positive $x$ -direction; wire 2 lies along the $y = 0$ line and carries a current in the negative $x$ -direction. What is the magnitude of the magnetic field at the point $(0 cm, 1 .5 cm, 0 cm)$ ?
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Textbook Question
A horizontal rectangular surface has dimensions 2.80 cm by 3.20 cm and is in a uniform magnetic field that is directed at an angle of 30.0° above the horizontal. What must the magnitude of the magnetic field be to produce a flux of 3.10 x 10^-4 Wb through the surface?
Textbook Question
Consider an electron undergoing cyclotron motion in a magnetic field. According to Bohr, the electron’s angular momentum must be quantized in units of ℏ. Compute the first four allowed radii in a 1.0 T magnetic field.
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Textbook Question
An electron experiences a magnetic force of magnitude 4.60 x10^-15 N when moving at an angle of 60.0° with respect to a magnetic field of magnitude 3.50 x 10^-3 T. Find the speed of the electron.
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Multiple Choice
A wire carries a positive current to the left in the plane of this screen. What is the direction of the magnetic field at a point near the top of the screen, still in the plane of the screen?
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Textbook Question
A circular area with a radius of 6.50 cm lies in the xy-plane. What is the magnitude of the magnetic flux through this circle due to a uniform magnetic field B = 0.230 T at an angle of 53.1° from the +z-direction?