Bozo's queries

[Bozo]

uh yeah, shiet did a typo on calc.

As for 17, imagine the ring dropping veritcally infront of her cutting the magnetic field. Since the magnetic field lines are running from the magnet i.e towards her (head on), use your right hand grip rule and pretend your the teacher standing there. The field lines are going to be running into you so your thumb will be facing the right direction ( i.e fist upside down). Hence the current will flow anti clockwise. If that doesn't make sense i'll draw a diagram.

[HarveyD]

yeah i think i need the diagram

[Bozo]

Maybe this will make more sense?

I can't draw 3D, so yeah hopefully this will make you understand.

Imagine as if the hand is horizontal matching the field lines exactly.

[HarveyD]

ah, but how do we know that lines run towards her rather than away from her?

[Bozo]

Its coming from the magnet as stated in the question. So it can only run towards her.

[HarveyD]

ohh okay
with this one:
wouldnt the brightness increase since theres more current running through it ---> More power?

[Bozo]

The answers D, since globe A burns out it is now an open circuit. The other two rows will be normally lit as they will receive an equal amount of voltage.

[HarveyD]

does that mean brightness is proportional to only the voltage and not the current?

[Bozo]

Shouldn't the answer to this be D, because the magnets repel each other and the magnetic field lines crossing over the compass will be in the southerly direction?

Am I missing something?

They say the answer is B =S

[Bozo]

Another question, is there a difference in the actual value of a de Broglie wavelength and a normal wavelength?

Because for on question i was given the energy and momentum of X-ray photons. Then i was asked what the wavelength of the X-rays was, so i went straight to lamda=h/p (using the momentum), but in the solutions they used the energy and it gives an answer that varies by .37???

[Lasercookie]

Another question, is there a difference in the actual value of a de Broglie wavelength and a normal wavelength?

Because for on question i was given the energy and momentum of X-ray photons. Then i was asked what the wavelength of the X-rays was, so i went straight to lamda=h/p (using the momentum), but in the solutions they used the energy and it gives an answer that varies by .37???

No there isn't any difference. What I think is happening is that trial exams give us rounded off values sometimes which leads to the small differences. That's my theory anyway.

[Bozo]

Just if you didn't see, look at 2 posts up, I had another question.

But .35 is a huge difference.

[Lasercookie]

Just if you didn't see, look at 2 posts up, I had another question.

But .35 is a huge difference.

Yeah, but if you calculate stuff yourself (and not round off), you'll find that both methods give the same answer.

The two equations can actually be derived from one another:

(since we're talking about photons)
If you did relativity then you would be familiar with



Which gets us:
Compton's equation:
de Broglie: 

E=pc is just e=mc^2=mc*c, mc is momentum so e=pc.

I've got further proof that the momentum value supplied by STAV is incorrect.
So the energy is . Let's figure out the momentum our selves.
(we can't use our regular kinetic energy equation - we're talking about photons here).


Now plug this into the debroglie equation. What do you get? The same answer for both methods.


Just speculating here: but in STAV's defence, they might have used a more accurate value for the speed of light. Perhaps that's what gave us the different answers.

[Lasercookie]

Oh yeah, that other question.

A compass needle points towards the south pole. (the north end of a compass needle is north).
So that's what it would point up, towards the southerly field lines.

More on the momentum/energy, it could be the energy calculation that's wrong (you can go figure it out based on the momentum) - either way I'm sure that one of the values provided in the question is wrong.

[Bozo]

Hmm, so it should produce the same answer, thats what I always though aswell.

BTW what did you get for this exam, i thought it was fairly easy (STAV 08)