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