Exam 20: Magnetism

A ring with a clockwise current (as viewed from above the ring) is situated with its center directly above another ring, which has a counter-clockwise current, as shown in the figure. In what direction is the net magnetic force exerted on the top ring due to the bottom ring?

At a point $10 \mathrm {~m}$ away from a long straight thin wire, the magnetic field due to the wire is $0.10 \mathrm { mT }$ . What current flows through the wire? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

An ideal solenoid with 400 turns has a radius of $0.040 \mathrm {~m}$ and is $40 \mathrm {~cm}$ long. If this solenoid carries a current of $12 \mathrm {~A}$ , what is the magnitude of the magnetic field at the center of the solenoid? $\left( \mu _ { 0 } = 4 \pi \right.$ $\times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A }$ )

A singly-charged ion enters a velocity selector that has a $0.18 - T$ magnetic field perpendicular to an electric field of $1.6 \mathrm { kV } / \mathrm { m }$ , with both fields perpendicular to the velocity of the ion. The same magnetic field is then used to deflect the ion into a circular path of radius $12.5 \mathrm {~cm} . \left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$ (a) What velocity was selected by the velocity selector? (b) What was the mass of the ion?

What is the magnetic moment of a rectangular loop having 120 turns that carries $6.0 \mathrm {~A}$ if its dimensions are $4.0 \mathrm {~cm} \times 8.0 \mathrm {~cm}$ ?

The direction of the force on a current-carrying wire in a magnetic field is

A high power line carries a current of $1.0 \mathrm { kA }$ . What is the strength of the magnetic field this line produces at the ground, $10 \mathrm {~m}$ away? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right.$ )

An ideal solenoid having 200 turns and carrying a current of $2.0 \mathrm {~A}$ is $25 \mathrm {~cm}$ long. What is the magnitude of the magnetic field at the center of the solenoid? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

A proton is accelerated from rest through 0.50 kV. It then enters a uniform magnetic field of 0.30 T that is oriented perpendicular to its direction of motion. (a) What is the radius of the path the proton follows in the magnetic field? (b) How long does it take the proton to make one complete circle in the magnetic field?.

A proton moving with a velocity of $4.0 \times 10 ^ { 4 } \mathrm {~m} / \mathrm { s }$ along the $+ y$ -axis enters a magnetic field of $0.20 \mathrm {~T}$ directed towards the $- x$ -axis. What is the magnitude of the magnetic force acting on the proton? $( e$ $= 1.60 \times 10 ^ { - 19 } \mathrm { C }$ )

An electron moves with a speed of $5.0 \times 104 \mathrm {~m} / \mathrm { s }$ perpendicular to a uniform magnetic field of magnitude $0.20 \mathrm {~T}$ . What is the magnitude of the magnetic force on the electron? $\left( e = 1.60 \times 10 ^ { - 19 } \right.$ C)

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 is parallel to the field. At that instant, what is the magnitude of the torque acting on the wire due to the magnetic field?

An electron moving in the $+ y$ direction, at right angles to a magnetic field, experiences a magnetic force in the $- x$ direction. The direction of the magnetic field is in the

A 2.0-m straight wire carrying a current of 0.60 A is oriented parallel to a uniform magnetic field of 0.50 T. What is the magnitude of the magnetic force on it?

A long, straight wire carrying a current is placed along the y-axis. If the direction of the current is in the +y direction, what is the direction of the magnetic field due to this wire as you view it in such A way that the current is coming directly toward you?

A flat coil containing 25 identical loops carries $6.4 \mathrm {~A}$ of current. When it is placed in a uniform magnetic field of $0.22 \mathrm {~T}$ that is oriented parallel to the plane of the coil, the magnetic torque on it is $3.7 \mathrm {~N} \cdot \mathrm { m }$ . (a) What is the magnetic moment of the coil? (b) What is the area of each loop?

A long wire carrying a $2.0$ -A current is placed along the $y$ -axis. What is the magnitude of the magnetic field at a point that is $0.60 \mathrm {~m}$ from the origin along the $x$ -axis? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

A flat circular loop of wire of radius $0.50 \mathrm {~m}$ that is carrying a $2.0$ -A current is in a uniform magnetic field of $0.30 \mathrm {~T}$ . What is the magnitude of the magnetic torque on the loop when the plane of its area is perpendicular to the magnetic field?

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 $0.50 \mathrm {~T}$ magnetic field to a final orbit radius of $0.50 \mathrm {~m}$ . The field is perpendicular to the velocity of the particles. What is the kinetic energy of an alpha particle in the final orbit? $( 1 \mathrm { eV } =$ $\left. 1.60 \times 10 ^ { - 19 } \mathrm {~J} , e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

A charged particle moving along the $+ x$ -axis enters a uniform magnetic field pointing along the $+ z$ -axis. Because of an electric field along the $+ y$ -axis, the charge particle does not change velocity. What is the sign of this particle?