# Homework Assignment

Chapter 29, Magnetic Fields

Questions 1, 2, 3, 4, 5, 18, 21

Problems   2, 8, 11, 12, 13, 20, 28, 31

Q1 At a given instant, a proton moves in the positive x cirection in a region where there is a magnetic field in the negative z direction. What is the direction of the magnetic force? Does the proton continue to move in the positive x direction?

Q2 Two charged particles are projected into a region where there is a magnetic field perpendicular to their velocities. If the charges are deflected in opposite directions, what can you say about them?

Q3 If a charged particle moves in a straight line through some region of space, can you say that the magnetic field in that region is zero?

Q4 Suppose an electron is chasing a proton up this page when suddenly a magnetic field is formed perpendicular to the page. Whast happens to the particles?

Q5 Why does the picture on a TV screen become distored when a magnet is brough near the screen?

Q18 The bubble chamber is a device used for observing tracks of particles that pass through the chamber, which is immersed in a magnetic field. If some of the tracks are spirals and others are straight lines, what can you say about the particles?

Q21 The electron beam if Figure 29.26 is projected to the right. The beam deflects downward in the presence of a magnetic field produced by a pair of current-carrying coils.

(a) What is the direction of the magnetic field?

(b) What would happen to the beam if the current in the coils were reversed?

29.2 An electron moving along the positive x axis perpendicular to a magnetic field experiences a magnetic deflection in the negative y direction. What is the direction of the magnetic field?

29.8 An electron is projected into a uniform magnetic field B = (1.4 i + 2.1 j) T. Find the vector expression for the force on the electron when its velocity is v = 3.7 x 105 j m/s.

29.11 Show that the work done by the magnetic force on a charged particle moving in a magnetic field is zero for any displacement of the particle.

29.12 A wire 40 cm long carries a current of 20 A. It is bent into a loop and placed with its plane perpendicular to a magnetic field having a flux density of 0.52 T. What is the torque on the loop if it is bent into

(a) an equilateral triangle,

(b) a square,

(c) a circle.

(d) Which torque is greatest?

29.13 A wire carries a steady current of 2.4 A. A straight section of the wire is 0.75 m long and lies along the x axis within a uniform magnetic field, B = (1.6 k) T. If the current is in the + x direction, what is the magnetic force on that section of wire?

29.20 A rod of mass 0.72 kg and radius 6.0 cm rests on two parallel rails (Fig P29.20) that are d = 12 cm apart and L = 45 cm long. The rod carries a current I = 48 A in the direction shown and rolls along the rails without friction. If the rod starts from rest, what is its speed as it leaves the rails if there is a uniform 0.24-T magnetic field directed perpendicular to the rod and the rails?

29.28 The magnetic field of the Earth at a certain location is directed vertically downward and has a magnitude of 0.5 x 10 - 4 T. A proton is moving horizontally towards the west in this field with a speed of 6.2 x 106 m/s.

(a) What are the direction and magnitude of the magnetic force the field exerts on this charge?

(b) What is the radius of the circular arc followed by this proton?

29.31 A proton moving in a circular path perpendicular to a constant magnetic field takes 1.00 microseconds to complete one revolution. Determine the magnitude of the field.