| QUIZ 20 CHS. 20 |
| QUIZ 20 |
| Do magnetic monopoles exist? |
|
SELECTED DISCUSSIONS TO exercises/problems
BELOW.
YOU ARE RESPONSIBLE FOR ALL PROBLEMS EVEN THE ONES WITHOUT DISCUSSIONS, WHICH ARE DESIGNED TO HELP YOU DO RELATED EXERCISES. Each sublist is separated by a semi-colon ";" and ends with the name of the section for those exercises. WE WILL REVIEW THEM IN-CLASS THE LAST WEEK BEFORE FINAL EXAM. |
| CH. 20 |
| CH. 20 MULTIPLE CHOICE TBA - Exercise/problems FIELD
AND FORCES 3, 9, 11; MOTION IN FIELD: 16, 18; MAGNETIC FORCE ON A WIRE 31, 32, 78 TORQUE ON A LOOP 34, 35 FIELD OF LONG WIRE 50; FORCE BETWEEN PARALLEL WIRES 53, 54 CURRENT LOOPS AND SOLENOIDS 57, 62 , 67, 82 FIELD CALCULATIONS 71 |
| TURN IN: 9, 16, 31, 78, 34, 50, 53, 67, 82, 71 |
| * DISCUSSIONS PROVIDED SOON |
| 9. Since the vector V is in the y direction and vector B lies in the x-y plane the force points in the be negative z direction, ( along your right thumb) wrap the velocity into the magnetic field vector with your right fingers. See equation 20.1; the angle between vector V and field B is shown in diagram. Force = mass *acceleration. |
| 16. See section 20.3. One-quarter of full circle circumference = pi*R/2 = 0.0118 m allows you to get R. See equation 20.4; from that relation you can get B. |
| 31. EQUATION 20.7. The force on segment ab is IN, by wrapping right ward I into downward B; the force on segment cd is in the opposite direction, OUT, with the same magnitude as the force on ab.. The force on segments bc and da are ZERO since the currents are parallel to the magnetic field. NOTE THE TWO NON-ZERO FORCE PRODUCE A TORQUE, CAUSING LOOP TO ROTATE LIKE AN ELECTRIC MOTOR. |
| 78. (a) The weight is DOWN, so the magnetic FORCE is UP. THE CURRENT MUST FLOW RIGHTWARD through the bottom bar. Thus, terminal a is at the higher voltage. (b) force magnitude = ILB =mg, where I = V/R and m is the maximum force. |
| 34. SEE PROBLEM 31; FORCE on segment bc and da are zero since wire segments are parallel and anti-parallel to the field. The only force exerting a torque about the hinge is on segment cd. THAT FORCE IS IS OUT. Torque = (0.350 m)*force, where force ILB. |
| 50. (a) Let us look at point Q; The upward
current causes an outward B field and the rightward current causes an
outward field. Use equation 20.10; since the fields are in the same
outward direction, just add them. AT P, the upward current causes an inward field, and the rightward current also causes an inward field; Again, use equation 20.10; since the fields are in the same inward direction, just add them. (b) Use the same method as in part (a); but you may not simply add them to get the correct answer since the field directions may be different this time around. |
| 53. Currents in same direction means wires attract; current in opposite directions means wires repel. Use eqn. 20.11 |
| 67. (a) Use eqn. 20.12. (b) Use eqn. 20.14; note n = N/L, where N = 1000 and length L is given. |
| MORE TO COME. CHECK BACK LATER. |