The h Bar

enumaris

5:01 PM

en.wikipedia.org/wiki/Force_between_magnets <--- so does that "prove" the statement "magnetic fields do no work" false?

0celo7

Why don’t magnets do work?

John Rennie

@enumaris the statement is meaningless rather than false. It's meaningless without some context.

0celo7

@BalarkaSen it’s just a section of the U(1) part of the Spin^C bundle

John Rennie

After all electric motors work using magnetic fields and electric motors can do work. Just ask Elon Musk :-)

enumaris

Usually the statement "magnetic fields do no work" is accompanied by the observation that the Lorentz force is given by $F=q(v\times B)$ (might be a minus sign) and then seeing that the force is always perpendicular to the velocity so $F\cdot v=0$ and so "magnetic fields do no work"

Sid

5:04 PM

@JohnRennie How can we show that two wave functions can cause interference?

Anonymous

Basically magnetic fields can store energy, which can be converted to mechanical work later on.

John Rennie

@enumaris Right. So the statement actually means the Lorentz force does no work. Which is where we came in.

Anonymous

@Sid Just add them up! (the wave equations) :P

John Rennie

@Sid Just add them together ...

Sid

Yes. And after that?

Balarka Sen

5:05 PM

Sum of two periodic waves is again a periodic wave

It's a small calculation

John Rennie

@Sid then square the modulus of the sum to determine the probability of finding the particle.

peterh

@BalarkaSen Except if the ratio of their periods is irrational. :-)

Balarka Sen

I had in mind a period of $2\pi$ for both

But yeah

Sid

Ah ha. Understood.

(That was a question in my semester exam today...)

enumaris

hmmm

Anonymous

5:09 PM

There nothing much to it other than some trigonometric identities

enumaris

I've been told again and again during my undergrad and grad careers that "magnetic fields do no work" and it's always the electric field "component" that does the work. And somehow it seemed like this was a rigorous statement.

Now it seems the statement is not rigorous at all...-.-

John Rennie

Life's like that sometimes

Anonymous

@enumaris Yeah, so don't believe people blindly :P

Balarka Sen

@Blue It's kind of fun to see that the effect of interference is vector addition on the pair (amplitude, phase angle)

Sid

@Blue well... yeah. But, when you see a question out of the blue(pun completely intended. :P) in the tense situation of an exam hall, stupidity is almost natural

Anonymous

5:12 PM

@BalarkaSen Right. It can be treated as phasors or complex addition (vector addition) too! Phasors are useful for AC current analysis and stuff :)

Balarka Sen

Yep

John Rennie

@BalarkaSen my goodness, is the appeal of physics luring you out of the hallowed halls of mathematics? :-)

0celo7

Why doesn’t the Lorentz force do work

What are you people talking about

CooperCape

Can you guys tell me if I'm overreacting about something for me... 'cause I'm kinda really mad and I don't have a clue what to think...

Balarka Sen

Lorentz force acts perpendicular to the displacement of the charged particle d00d

The dot product is 0

Sid

5:13 PM

@CooperCape yep. You are overeacting

Balarka Sen

lol

CooperCape

:C

K then

Balarka Sen

@JohnRennie On the contrary, I want to #MakePhysicsGreatAgain

CooperCape

thanks <3

Phase

@CooperCape wus poppin bruv

Anonymous

5:14 PM

@JohnRennie All mathematicians like physics. Some just don't admit it. :P

enumaris

hmmm

0celo7

@Blue that is patently false

enumaris

I'm gonna have to reevaluate my life

0celo7

Please think before making sweeping generalizations.

Anonymous

@0celo7 See, you're the living proof

CooperCape

5:15 PM

Okay so basically my friend was being imo a massive @$%& (insert whatever 4 letter noun you wish) and he basically over the course of an hour was just giving me loads of shit for like no reason culiminating in 4 main phrases we have...

Phase

Well, first step is communicate about how he pissed you off

CooperCape

"Your girlfriend fancies *someone*.... I'm sure" and that I should confront her about it...

Phase

and take it from there when you see your reaction

CooperCape

"I'm gonna tell her she doesn't like you as much as she says she does"

Phase

Your friend sounds like an ass

enumaris

5:16 PM

there's 2 possibilities

CooperCape

I don't know what to dooooo

0celo7

I openly like physics.

Balarka Sen

ah teenage love life

John Rennie

@CooperCape he isn't your friend. Walk away.

Sid

If he is a very good friend, he might just be pulling your leg.

CooperCape

5:16 PM

@BalarkaSen Ikr... classic

Anonymous

Gosh. Teenage love issues are always pretty complicated

enumaris

1. he knows she's cheating on you and that's what's happening. 2. He's jealous or something or he's an ass

Phase

I second JR's motion

Anonymous

And I'm awful at these stuff XD

CooperCape

He just sounded dead serious

Sid

5:17 PM

If he is not, well then, he is not your friend...

enumaris

If it's option 1. tho....then it's the gf that's the problem

John Rennie

46 secs ago, by John Rennie

@CooperCape he isn't your friend. Walk away.

enumaris

If it's option 2. go with JR's suggestion

Sid

(And no, you are not overreacting.)

enumaris

Probably you have to make the distinction of whether it's more likely your friend is telling the truth or not

we don't know your friend

0celo7

5:18 PM

There are those who truly dislike physics and for you to claim they like it is insulting

@Blue

enumaris

super insulting?

Sid

and also how much you trust your girlfriend..

CooperCape

I mean I trust her a lot

enumaris

indeed

CooperCape

Pretty sure nothing's going on there

Anonymous

5:19 PM

@0celo7 We'll never know ;)

Phase

Rumours spread incredibly fast in high school, and rarely is there ever any merit with it

Sid

Is it an old friend?

CooperCape

Might just leave it until tomorrow see what happens. If he brings it up again I'ma just leave...

Phase

If you're concerned, talk to your gf about it

Balarka Sen

Why would Blue insult me by calling me a "physicist" when I would NEVER call him "incapable of being a mathematician"? Oh well, I try so hard to be his friend - and maybe someday that will happen!

CooperCape

5:20 PM

I would but I don't wanna make her needlessly mad yano

enumaris

so ask for concrete proof that she's cheating on you, if your friend can't supply it, ask him if it's just rumor. Maybe option 3 is, he's not an ass, but just really gullible to rumors?

CooperCape

It's not even a rumour

John Rennie

@enumaris no, don't do that.

CooperCape

Pretty sure he just pulled it out of no where

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