D. Magnetism Part II (19.4-195)

50 points

 

19.4 Magnetic Materials

42, 43, 44, 45, 47

45:  Recall that electron orbits are counter to the direction of the current.  Current flows from + to – terminals.  Electrons, however, flow from – to + terminals.

47:  F = mv2/r = kq1q2/r2 where q1=q2=1.6x10-19C.  melectron = 9.11x10-31 Kg. 

nm = 10-9m.  K = 9 x 109 Nm2/C2.  Solve for velocity.  Once you get that, realize that

I = q/t where we can assume t to equal the period (T - # of seconds/1 rotation). 

So, I = q/2pr/v.   Finally, B =moI/2r.

     Wow!!   What a great quiz question!  It uses multiple steps and involves some old Newton’s laws formulas!!

 

19.5:  Magnetic forces on current-carrying wires

49, 50, 51, 52, 54, 57, 63, 65, 67, 70

50:  Currents are in the same direction

54:  point right thumb in direction of force.  Point fingers along I (which is not shown in the diagram) and curl fingers to the B direction (which is shown)

57:  point right thumb along I.  Straight fingers along B (given) and curl to find direction of Force.

63:  fingers point in direction of I, curl in direction of B.  Thumb points to force.

65:  look at example 19.5 on p. 612 – it is very similar!

67:  use F = ILBsinq where q = 90o each time (prove to yourself why this is the case each time).  Use the right hand rule to determine whether it is attractive or repulsive

70:  Remember that q is the angle between a Normal line to the plane of the loop (Normal lines are ^ to the plane – remember “Normal force” being ^ to the plane of the Earth?) and the B field.  The angle given in the problem is the angle between the plane of the loop and the B field (this is 90o different from the Normal line and the B field)

 

Even Answers:

42:  b

44:  toward you

50:  it shortens

52:  1.5N in +y direction (realize that this problem is asked in a funny way – not “ha, ha” funny, but “poorly” funny.  If you draw out the x,y,z coordinate board where –z is straight down – as opposed to into the page as we are accustomed, you will see that the orientation of +y is into the page not out of the page).

54:  a) right   b) toward the top of the page   c)  into the page   d) left   e) into or out of the page since the current must be parallel to the B field as there is no force.  Parallel to the B field could be in either direction.

70:  0.013 mN