/0's physics phread

[/0]

thanks tt

also,

"A magnet falling through a metal tube can achieve terminal velocity. Why?"

Is this an apt description?

The magnet induces a magnetic field in the metal of the tube. Due to the magnet's velocity relative to the external magnetic field, its charges are separated. The seaparation of charges also means that, by the right-hand slap rule, the external magnetic field exerts an upward force on the magnet. When the speed of the magnet reaches a certain point, the upwards magnetic forces balances the gravitational force, so terminal velocity is achieved.

Is there a better way to explain it?

[TrueTears]

Yeap, that's fine, just remember that also as the rod falls faster and faster the magnetic force on it increases (F = Bqv). The rod will achieve terminal velocity once the magnetic force equals the weight force.

Other than that, your explanation is fine. Very detailed.

[/0]

thanks again TT

If you have a circular loop completely immersed in a magnetic field and you move it out of the field.
Inside the loop,
But outside the loop, as well...

Why are we only concerned with the inside the loop?

NVM WORKED IT OUT

[TrueTears]

thanks again TT

If you have a circular loop completely immersed in a magnetic field and you move it out of the field.
Inside the loop,
But outside the loop, as well...

Why are we only concerned with the inside the loop?

What do you mean by loop? loop of wire? loop with current through it?

[Mao]

How does AC current actually work? If the current goes back and forth then how does it get anywhere?

Electric power comes from motion of electrons. In this case, the overall motion of electrons in AC current is nought, but it can be described as oscillations, which is still a type of motion, hence there is electric power.

[/0]

How does AC current actually work? If the current goes back and forth then how does it get anywhere?

Electric power comes from motion of electrons. In this case, the overall motion of electrons in AC current is nought, but it can be described as oscillations, which is still a type of motion, hence there is electric power.

woah that's sick as, thx man

thanks again TT

If you have a circular loop completely immersed in a magnetic field and you move it out of the field.
Inside the loop,
But outside the loop, as well...

Why are we only concerned with the inside the loop?

What do you mean by loop? loop of wire? loop with current through it?

Just like Q8 Page 274

I was wrong... outside the loop



Another:

Two coils are placed one on top of the other with their centres in line.
(a) If a battery is switched on in the bottom coil, producing a clockwise current as seen from above, what happens in the top coil?
(b) Would the effect be different if the battery was connected to the top coil?
(c) Would the effect be different if the battery was switched off?

Are the answer (a) nothing (b) no (c) no ?
Because in (a) the top coil isn't moving so i would think that means there's no force?
And in (b) The bottom coil isn't moving so the top coil does no force on the bottom?
And in (c) nothing happens anyway?

[TrueTears]

Oh okay, here's how I did the question.

negative number (Since )

Let into page be +ve.

So must be out of page. Induced magnetic field must be into the page (opposite direction)

Using right hand grip rule, current goes clockwise

[TrueTears]

How does AC current actually work? If the current goes back and forth then how does it get anywhere?

Electric power comes from motion of electrons. In this case, the overall motion of electrons in AC current is nought, but it can be described as oscillations, which is still a type of motion, hence there is electric power.

woah that's sick as, thx man

thanks again TT

If you have a circular loop completely immersed in a magnetic field and you move it out of the field.
Inside the loop,
But outside the loop, as well...

Why are we only concerned with the inside the loop?

What do you mean by loop? loop of wire? loop with current through it?

Just like Q8 Page 274

I was wrong... outside the loop



Another:

Two coils are placed one on top of the other with their centres in line.
(a) If a battery is switched on in the bottom coil, producing a clockwise current as seen from above, what happens in the top coil?
(b) Would the effect be different if the battery was connected to the top coil?
(c) Would the effect be different if the battery was switched off?

Are the answer (a) nothing (b) no (c) no ?
Because in (a) the top coil isn't moving so i would think that means there's no force?
And in (b) The bottom coil isn't moving so the top coil does no force on the bottom?
And in (c) nothing happens anyway?

Okay here is how I did the question.

a)

Bird's eye view of the diagram.

Now, lower coil the magnetic field is into the page, using RHGR

now there must be a induced magnetic field in the upper coil. First lets find the direction of change in flux.

let into the page be +ve

lets work out change in flux for lower coil

flux final - flux initial, it is positive since flux final > flux initial, so that means induce mag field is opposite direction, so its out of page, now if it is out of page lets use RHGR on upper coil
 
Therefore current is anti clockwise for upper coil.

 

[/0]

OH, so we are looking at the short time between the battery being off and the battery being on, cool thanks bro

But the current in the top wire should only be for a split second, right? Because as soon as the battery is on the magnetic field will become constant?

[TrueTears]

Yeap that's right

[/0]

thxthxthxthxthxthxthxthxthxthxTT

How can a motor operate as a DC generator?

[TrueTears]

I thought generators are AC lol

[/0]

Hmmm that's interesting. it's Q15 pg 274
Might have to ask the BMW

[TrueTears]

Hmmm that's interesting. it's Q15 pg 274
Might have to ask the BMW

Hmmm I think maybe change the split rings to slip rings? Dono but that makes a AC generator lols.

[/0]

OK, I have an interesting conundrum...

Say you have a rectangular wire loop lying horizontal which is COMPLETELY immersed in an infinite, uniform, perpendicular magnetic field.

If you move the wire, according to F = Bqv, the charges should separate, and hence there must be an emf.

However, according to Lenz's Law, no matter where you move this wire, the flux through the wire will always be the same, because the magnetic field is uniform. Thus, there should be no emf.

How can this be resolved?