1) in the direction marked 1 2) in the direction marked 2 3) in the direction marked 3 4) out of the page 5) into the page

Transcription

1 Q1) In the figure, the current element i dl, the point P, and the three vectors (1, 2, 3) are all in the plane of the page. The direction of db, due to this current element, at the point P is: 1) in the direction marked 1 2) in the direction marked 2 3) in the direction marked 3 4) out of the page 5) into the page Q2) A cross section of the magnetic field for a current-carrying wire is shown. The direction of the current is 1) to the left. 2) to the right. Q3) Which graph correctly gives the magnitude of the magnetic field outside an infinitely long straight currentcarrying wire as a function of the distance r from the wire?

2 Q4) The figure below shows four arrangements in which long parallel wires carry equal currents directly into or out of the page at the corners of identical squares. Rank the arrangements according to the magnitude of the net magnetic field at the center of the square, greatest first. 1) c, d, a = b 2) c, a = b, d 3) d, c, a = b 4) a, d, b = c 5) a = b = c = d Q5) Four long parallel wires pass through the four corners of a square. All four wires carry the same amount of current and the current directions are as indicated. What is the direction of the magnetic field at the center of the square? 1) up 2) down 3) right 4) left Q6) Two conducting wires perpendicular to the page are shown in cross section as gray dots in the figure. They each carry a current out of the page. What is the direction of the magnetic field at point P? 1) up 2) down 3) right 4) left Q7) A battery establishes a steady current around the circuit below. A compass needle is placed successively at points P,Q, and R. The relative deflection of the needle, in descending order, is 1) P, Q, R. 2) Q, R, P. 3) R, Q, P. 4) P, R, Q. 5) Q, P, R.

3 Q8) The figure below shows three circuits, consisting of concentric circular arcs (either half- or quarter-circles of radii r, 2r, and 3r) and radial lengths. The circuits carry the same current. Rank them according to the magnitude of the magnetic field produced at the center of curvature (the dot) greatest first. 1) a = b, c, 2) b, a, c 3) a, b, c d 4) a, c, b Q9) Which point A or B has the larger magnetic field? 1) A 2) B 3) B-field is the same at A and B. I I B A Q10) In all cases the wire shown carries a current I. For which situation is the magnitude of the magnetic field maximum at the point P? Q11) Two parallel wires carry identical upward currents, as shown. Does the Coulomb force between the downward moving, negatively charged electrons in each wire cause a repulsive force between the wires? 1) Yes, but the magnetic force is stronger 2) Yes, but only if I is sufficiently small 3) No, moving charges don't exert a Coulomb force on each other 4) None of the above

4 Q12) The figure below shows four identical currents i and five Amperian paths encircling them. Rank the paths according to the value of B ds taken in the directions shown, most positive first and most negative last. 1) all tie 2) a, b = d, c, e 3) d, a = c = e, b 4) d, a = e, b, c 5) c, b, a = e, d Q13) If the magnetic field B is uniform over the area bounded by a square with edge length a, the net current through the square is 1) 0 2) 4 Ba/ 0 3) Ba 2 / 0 4) Ba/ 0 5) B/ 0 Q14) Two long solenoids are nested on the same axis as shown below. They carry identical currents but in opposite directions. If the magnetic field inside the inner solenoid is zero, what can you say about the number of turns per unit length for the two solenoids? Which one, if either, has a larger value? 1) the inner solenoid 2) the outer solenoid 3) neither, they are equal 4) not enough information given Q15) To double the magnetic field inside a solenoid you should 1) double the length, while keeping the number of turns per unit length constant. 2) double the number of turns while keeping the length constant. 3) double the length and the total number of turns. 4) two of the above Q16) Which one of the following statements concerning the magnetic field well inside a long, current carrying solenoid is true? 1) The magnetic field is zero. 2) The magnetic field is non-zero and nearly uniform. 3) The magnetic field is independent of the number of windings. 4) The magnetic field is independent of the current in the solenoid. 5) The magnetic field varies as 1/r as measured from the solenoid axis.

5 Q17) The figure below shows four arrangements of circular loops of radius r or 2r, centered on vertical axes and carrying identical currents in the directions indicated. Rank the arrangements according to the magnitude of the net magnetic field at the dot, midway between the loops, greatest first. 1) c, d, a, b 2) c, d, a = b 3) d, c, a, b 4) d, c, a = b 5) d, a, b = c Q18) Two loops carry equal currents I in the same direction. The loops are held in the positions shown in the figure and are then released. Which one of the following statements correctly describes the subsequent behavior of the loops? 1) Both loops move to the left. 2) The loops remain in the positions shown. 3) The top loop moves to the right; the bottom loop moves to the right. 4) The loops repel each other. 5) The loops attract each other. Q19) The geographic north pole of the earth is magnetically a 1) north pole 2) south pole Q20) If you place a chunk of iron near the south pole of a magnet, attraction will occur. Will attraction also occur if you place the iron near the north pole of a magnet? 1) yes 2) no Q21) Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a 1) north pole 2) south pole 3) north or south pole no difference really Q22) Which one of the following statements concerning permanent magnets is false? 1) The north pole of a permanent magnet is attracted to a south pole. 2) All permanent magnets are surrounded by a magnetic field. 3) The direction of a magnetic field is indicated by the north pole of a compass. 4) Magnetic field lines outside a permanent magnet originate from the north pole and end on the south pole. 5) When a permanent magnet is cut in half, one piece will be a north pole and one piece will be a south pole.

6 Q23) A permanent bar magnet is broken in half. The two pieces are interchanged, keeping their orientations fixed, as shown below. Do the pieces attract or repel? 1) Attract 2) Repel A long straight wire is carrying current I. The magnetic field at point x has magnitude B total. r B total x I r B 1/2 =? True (A) or False (B): The magnetic field B 1/ 2 B total same direction and has 1/2 the magnitude of. at point x due only to the current to the left of x points in the