Exam 20: Magnetism

What is the force per meter on a straight wire carrying $5.0 \mathrm {~A}$ when it is placed in a magnetic field of $0.020 \mathrm {~T}$ so that the wire makes an angle of $27 ^ { \circ }$ with respect to the magnetic field lines.

Which of the following are units for the magnetic moment? (There could be more than one correct choice.)

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions $w = 0.60 \mathrm {~m}$ and $L = 1.0 \mathrm {~m}$ , and carries a current $I = 2.0 \mathrm {~A}$ in the direction shown. The magnetic field due to the magnet is uniform and of magnitude $0.80 \mathrm {~T}$ . The loop rotates in the magnetic field and at one point the plane of the loop makes a $30 ^ { \circ }$ angle with the field. At that instant, what is the magnitude of the torque acting on the wire due to the magnetic field?

A flat circular loop carrying a current of $2.0 \mathrm {~A}$ is in a magnetic field of $3.5 \mathrm {~T}$ . The loop has an area of $0.12 \mathrm {~m} ^ { 2 }$ and its plane is oriented at a $37 ^ { \circ }$ angle to the field. What is the magnitude of the magnetic torque on the loop?

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long (to 2L), but all other quantities remained the same, the magnetic field inside the solenoid will

A rigid rectangular loop, measuring $0.30 \mathrm {~m}$ by $0.40 \mathrm {~m}$ , carries a current of $9.9 \mathrm {~A}$ , as shown in the figure. $\mathrm { A }$ uniform external magnetic field of magnitude $1.8 \mathrm {~T}$ in the $- x$ direction is present. Segment CD is in the $x z$ -plane and forms a $19 ^ { \circ }$ angle with the $z$ -axis, as shown. What is the $y$ component of the magnetic force on segment $A B$ of the loop?

A proton, starting from rest, accelerates through a potential difference of $1.0 \mathrm { kV }$ and then moves into a magnetic field of $0.040 \mathrm {~T}$ at a right angle to the field. What is the radius of the proton's resulting orbit? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } , m _ { \text {proton } } = 1.67 \times 10 ^ { - 27 } \mathrm {~kg} \right)$

The magnitude of the magnetic field that a long and extremely thin current-carrying wire produces at a distance of $3.0 \mu \mathrm { m }$ from the center of the wire is $2.0 \times 10 ^ { - 3 } \mathrm {~T}$ . How much current is flowing through the wire? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

Two long parallel wires carry currents of $20 \mathrm {~A}$ and $5.0 \mathrm {~A}$ in opposite directions. The wires are separated by $0.20 \mathrm {~m}$ . What is the strength of the magnetic field midway between the two wires? ( $\left. \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

A wire in the shape of an "M" lies in the plane of the paper. It carries a current of $2.0 \mathrm {~A}$ , flowing from $A$ to $\mathrm { E }$ . It is placed in a uniform magnetic field of $0.85 \mathrm {~T}$ in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that $A B$ is parallel to $D E$ and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the net force acting on this wire?

Alpha particles, each having a charge of $+ 2 e$ and a mass of $6.64 \times 10 ^ { - 27 } \mathrm {~kg}$ , are accelerated in a uniform $0.80$ -T magnetic field to a final orbit radius of $0.30 \mathrm {~m}$ . The field is perpendicular to the velocity of the particles. How long does it take an alpha particle to make one complete circle in the final orbit? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

A flat circular coil has 200 identical loops of very thin wire. Each loop has an area of $0.12 \mathrm {~m} ^ { 2 }$ and carries $0.50 \mathrm {~A}$ of current. This coil is placed in a magnetic field of $0.050 \mathrm {~T}$ oriented at $30 ^ { \circ }$ to the plane of the loop. What is the magnitude of the magnetic torque on the coil?

When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes

A straight wire is carrying a current of $2.0 \mathrm {~A}$ . It is placed at an angle of $60 ^ { \circ }$ with respect to a magnetic field of strength $0.20 \mathrm {~T}$ . If the wire experiences a force of $0.40 \mathrm {~N}$ , what is the length of the wire?

A rigid rectangular loop, measuring $0.30 \mathrm {~m}$ by $0.40 \mathrm {~m}$ , carries a current of $5.5 \mathrm {~A}$ , as shown in the figure. A uniform external magnetic field of magnitude $2.9 \mathrm {~T}$ in the $- x$ direction is present. Segment CD is in the $x z$ -plane and forms a $35 ^ { \circ }$ angle with the $z$ -axis, as shown. What is the magnitude of the torque that the magnetic field exerts on the loop?

The figure shows a velocity selector that can be used to measure the speed of a charged particle. A beam of particles of charge $+ q$ is directed along the axis of the instrument. A parallel plate capacitor sets up an electric field $E$ which is oriented perpendicular to a uniform magnetic field $B$ . If the plates are separated by $3.0 \mathrm {~mm}$ and the value of the magnetic field is $0.30 \mathrm {~T}$ , what potential difference between the plates will allow particles of speed $v = 5.0 \times 10 ^ { 5 } \mathrm {~m} / \mathrm { s }$ to pass straight through without deflection?

A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component

A wire along the $z$ -axis carries a current of $4.9 \mathrm {~A}$ in the $+ z$ direction. Find the magnitude and direction of the force exerted on a $3.3 - \mathrm { cm }$ long length of this wire by a uniform magnetic field pointing in the $- x$ direction having a magnitude $0.43 \mathrm {~T}$ .

A proton moving eastward with a velocity of $5.0 \mathrm {~km} / \mathrm { s }$ enters a magnetic field of $0.20 \mathrm {~T}$ pointing northward. What are the magnitude and direction of the force that the magnetic field exerts on the proton? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

The magnetic force on a current-carrying wire in a magnetic field is the strongest when