CHAPTER 19 REVIEW 1. The north pole of a magnet is attracted to the geographic North Pole of Earth. But like poles repel. Can you explain this? 2. A magnetized steel needle is placed in a Bunsen burner flame. It becomes demagnetized. Explain why. 3. A conductor carrying a current is arranged so that electrons flow in one segment from east to west. A compass is held over this segment of the wire. In what direction is the needle deflected? Recall that current is defined as the motion of positive charges. 4. On what factors does the strength of the magnetic field of a solenoid depend? 5. Suppose an electron is chasing a proton up the page of a book. Suddenly a magnetic field pointing into the page is applied. What happens to the particles? 6. Explain why two parallel wires carrying currents in opposite directions repel each other. 7. A duck flying due east passes over Atlanta. The magnetic field of Earth at that location is 5.0 x 10-T directed north. The duck has a positive charge of 4.0 x 10- C. The magnetic force acting on the duck is 3.0 x 10-1 N upward. What is the duck's velocity? 434 CHAPTER 198. Find the direction of the force on a proton moving through each magnetic field below. x x x x III XXXX' Bin a. x xx x b . Bout B 9. Assume that in each case above the velocity vector is replaced with a wire carrying a current in the direction of the velocity vector. Find the direction of the magnetic force acting on each wire. a. 10. A current of / = 15 A is directed along the positive x-axis and perpendicular to a uniform magnetic field. The conductor experiences a magnetic force per unit length of 0.12 N/m in the negative y-direction. Calculate the magnitude and direction of the magnetic field in the region the current passes through. 11. A proton is moving perpendicular to a magnetic field of strength 3.5 mT. It experiences a force due to the field of 4.5 x 10-21 N. Calculate the speed of the proton. Recall that a proton has a charge of 1.60 x 10- C. ARRANGEMENT OF ELECTRONS IN ATOMS 435