questions (1 Viewer)

[Arithela]

These questions have been bothering me for ages:


1. At a certain place on the earth's surface, the horizontal component of the earth's magnetic field is 4.5 x 10^-5 T. A wire oriented at right angles to this horizontal component is moving vertically so it cuts the field at right angles with a speed of 25m/s. If the wire is 12m long, what is the magnetic flux cut per second?

2. A square loop of wire, WXYZ, of side 0.10m is held at right angles to a magnetic field of intensity 4.0 x 10^-4 T. The field is directed down into the page and exists only to the left of the line AB.

(a)
(i) Explain why no current will flow in the loop until the side XY crosses the line AB.
(ii) Calculate the emf induced in the coil as the side XY crosses the line AB.
(iii) This emf produces an induced current that flows clockwise in the loop. Lenz's law state that an induced current flows in such a direction as to oppose the change that caused it. How does the clockwise-flowing current "oppose the change that caused it"?

(b) The loop is now moved back to its original position. The magnetic field is then steadily decreased to 1.0 x 10^-4 T over an inerval of 2.0 x 10^-3 s. Calculate the emf generated in the loop.

3. Graph the voltage vs time graph for a DC dynamo, an alternator and a battery.

4. Compare a split ring communtator with a slip rings, and give the application of each.


THANKS

 

[177152]

3.
The Alternator is a sine curve, Ie. the voltage reached in the positive direction is the same magnitude as the negative direction, oscillating between the two extremes.
The DC Dynamo is a little different, the voltage is always positve, it "Jumps" up to the max voltage and falls back down (Like a projectile, but steeper.) It keeps doing that...
Battery is just a straight line at the same voltage... Constant voltage.

4.
A split ring commutator consists of a brass ring separated in half by an insulator, set up so that as the armature rotates on the axle the current swaps direction to ensure positive torque, Ie. The halves of the commutator contact opposite brushes to ensure constant flow in the same direction in the armature (Relative to the stator). Used for DC motors... I'm not sure what I'd put for that part of the question.
As for slip rings, they're two full rings, each having a separate brush contacting it, the AC vibrates at the same rotational speed as the armature, thus ensuring positive torque (50Hz for household, 50 oscillations per second, the voltage that is.) The armature spins in time with that. It's used for AC and I suppose triple phase as well.(You may have to clarify that with someone who knows what they're doing)

Hope that's helped, I didn't answer the question for 4, but just use that information and compare them.

=]

 

[177152]

As for the other questions, Were there diagrams to go with? I'm a bit lost in the second one =)