can someone do this question...... (1 Viewer)

[Saintly Devil]

questions......

I need clarification on a number of questions, which I have found, and for which answers are not given.

1)The electron beam in a TV picture tybe can move across the screen faster than the speed of light. Why does this not violate the special theory of relativity?

2)Light cannot escape from black holes, yet they have been idetified with the help of X rays emitted as matter is sucked into them. How do you think X rays can escape whereas light cannot?

for 1), I thought it might be because the picture tube moves back and forth across the screen, meaning it changes direction, hence velocity and is hence accelerating. This would mean that it can't be considered an intertial frame of reference and hence does not violate the principle of the special theory of relativity. Is this remotely correct? Can anyone think of a better answer?

for 2) i'm totally stumped.


Thanks

 

[BlackJack]

1) Think about what you see. We see the beam 'move' across the screen, but really it's only the electrons hitting different phosphorus cells one after another, creating an illusion of movement.

All the electrons in the beam are still travelling at the same velocities as before, but just in different directions.

edit: since this change of direction is made with magnetic fields, the tube itself need not move at light-seed.

2) According to theory, black holes have 2 points (at the two poles of the stellar 'body') where they emit x-rays. when the black hole is 'consuming' something, some of the energy is radiated out along those 2 poles.

That allows detection if we are in hte path of those rays.

note: x-ray is just light with shorter wavelength.

 

[CHUDYMASTER]

For his second question, you haven't answered it, but merely restated what happens. The question is why light can't escape black holes yet X-rays can. This seems contradictory because both are EM radiation. And what's your point in mentioning that x-rays have higher frequencies?

 

[Saintly Devil]

also, for the first one, if the 'illusion of movement' is going faster than the speed of light (since the question states that at least something is going faster than the speed of light), then that must mean that the change in direction is faster than the speed of light ?!

also, what do you say about my theory - the change in direction means it is accelerating, hence the special theory of relativity doesn't apply - why is that wrong, if at all, it is?

 

[BlackJack]

For the black hole theory, we're steeping into muCh higer physics. X-rays aren't exempt from that gravity in any other circumstance, but the x-rays that we have spotted from the blackhole are (theoretically) created by the black hole when it 'consumes' matter, shooting out at the poles for some odd reason that I don't konw.

An in-depth scientific site might be what you're after from this point on.

---

The change in direction is faster than the speed of light, but since it's not a material object it is not subject to physics.
edit: your theory isn't wrong per se, any accelerating frame actually requires general relativity. However, I don't think applying this to the 'changing direction' , a radial movement, is a satisfying answer.

 

[Saintly Devil]

ahhh...........makes sense now.
thanks.

 

[Saintly Devil]

Some more questions i need confirmed, but about motors and generators this time:

1)A charged particle moves in a straight line through a particular region of space. Could there be a nonzero magnetic field in this region? If so, give two possible situations.

2)If a moving charged particle is deflected sideways in some region of space, can we conclude for certain that B does not equal 0 in that region?

3)If a negatively charged particle enters a region of uniform magnetic field which is perpendicular to the particle's velocity, will the kinetic energy of the particle increase, decrease or stay the same? Explain your answer (Neglect gravity)

 

[kini mini]

Originally posted by Saintly Devil
Some more questions i need confirmed, but about motors and generators this time:

1)A charged particle moves in a straight line through a particular region of space. Could there be a nonzero magnetic field in this region? If so, give two possible situations.

Yes - particle travelling parallel to field lines in either direction.

2)If a moving charged particle is deflected sideways in some region of space, can we conclude for certain that B does not equal 0 in that region?

If a charged particle is deflected, there could be an electric field, or a magnetic field, or even both.

3)If a negatively charged particle enters a region of uniform magnetic field which is perpendicular to the particle's velocity, will the kinetic energy of the particle increase, decrease or stay the same? Explain your answer (Neglect gravity)

When the particle enters the field it will be deflected from its original path - that's all I remember from the course . My guess is that the KE would increase because there is a force vector acting on the particle due to the B field that adds to the original vector. This, however, might well be completely wrong .

 

[professor]

mm...those questions sounds a lil bit too tough...dun tell me we need to know these for the HSC...

 

[Saintly Devil]

Originally posted by kini mini

Yes - particle travelling parallel to field lines in either direction.

Yeah...that's one. For the other one I thought maybe it could be when you have two magnets with like poles facing each other, there is a place right in the middle of them where perhaps the magnetic field is zero?

Yeah, i got this from a first year uni physics textbook. It has a lot of stuff outside the syllabus, but explains the content matter much better than jacaranda.

 

[kini mini]

Originally posted by Saintly Devil

Yeah...that's one. For the other one I thought maybe it could be when you have two magnets with like poles facing each other, there is a place right in the middle of them where perhaps the magnetic field is zero?

Sorry, I thought of one example and just moved on. There are quite a few ways to get magnetic fields to cancel each other out, have you been given any of those questions with perpendicular current-carrying and the resultant force on a charged particle at a point? Put equal forces on opposite vectors to the aprticle so they balance and they figure out where your field needs to be to get those forces.

Yeah, i got this from a first year uni physics textbook. It has a lot of stuff outside the syllabus, but explains the content matter much better than jacaranda.

Uni undergrad textbooks tend to be much better written than high school ones . For all the failings of the American high school system, the undergrad books produced for the colleges are of a very high quality.