Length contraction??? (1 Viewer)

[vnblueberry]

EXACTLY THE PROBLEM
glen and helper have different answers.
now until someone posts up the actual Q in its hard copy form, there is little use in its discussion.

 

[helper]

The question as I posted is a direct OCR of the paper. I have also posted the paper
http://community.boredofstudies.org/686/physics/125704/part-b-question-paper.html

 

[XcarvengerX]

For those who got 0.3m, was your answer for mass (part b) increasing or decreasing?

 

[bboyelement]

ok. this question is simple you just have to get your head around it. from the particles perspective (which is travelling at 0.6c) the length of anode to cathode is contracted. just imagine it this way, the electron particle is standing still and the anode and screen is moving at 0.6c, as it is travelling at that speed pass the electron it should be contracted, if viewed from the electron. ok so if 0.24 is the contracted length then it must be greater than 0.24 so 0.19 is not an answer for the proper length.

just must note that there is no absolute frame of reference, relavistic effects are reversible if viewed from a different frame.

it is 0.3

 

[raikkonen_rulez]

ok. this question is simple you just have to get your head around it. from the particles perspective (which is travelling at 0.6c) the length of anode to cathode is contracted. just imagine it this way, the electron particle is standing still and the anode and screen is moving at 0.6c, as it is travelling at that speed pass the electron it should be contracted, if viewed from the electron. ok so if 0.24 is the contracted length then it must be greater than 0.24 so 0.19 is not an answer for the proper length.

just must note that there is no absolute frame of reference, relavistic effects are reversible if viewed from a different frame.

it is 0.3

Please do yourself. I'm sure the answer is .192m. I read the question more than 5 times, since the electron cannot do any experiments or calculations or blah to tell if it's travelling at constant speed, it cannot detect any changes to its "rest length", it's Lv we're looking for, not Lo.

 

[P_Dilemma]

Please do yourself. I'm sure the answer is .192m. I read the question more than 5 times, since the electron cannot do any experiments or calculations or blah to tell if it's travelling at constant speed, it cannot detect any changes to its "rest length", it's Lv we're looking for, not Lo.

We're not debating whetheror not electrons have the capacity to be aware of their situation. The question said that from it's perspective (at 0.6c) it would experience the length travelled as 24 cm.

From the outside perspective the distance would be longer, as in a relativistiv framve of reference all lengths seem shorter.

The answer of 30cm, or 0.3m. QED.

-P_D

 

[helper]

Please do yourself. I'm sure the answer is .192m. I read the question more than 5 times, since the electron cannot do any experiments or calculations or blah to tell if it's travelling at constant speed, it cannot detect any changes to its "rest length", it's Lv we're looking for, not Lo.

Your not measuring the rest length of the electron. You are measuring the length between the anode and the screen. This is moving wrt the electron, so assuming the electron can observe as it states in the question, then it will be contracted as observed by the electron.

 

[dunno04]

Please do yourself. I'm sure the answer is .192m. I read the question more than 5 times, since the electron cannot do any experiments or calculations or blah to tell if it's travelling at constant speed, it cannot detect any changes to its "rest length", it's Lv we're looking for, not Lo.

wel
WE are in the same boat!

I got the same answer

The question is so gawd dam confusing!
+.+

 

[doraemon]

just pretend there is a ruler in our frame of reference. the electron who is moving 0.6c to it, sees the 30cm ruler contract to 24cm. we see the 30cm ruler as 30 cm.

 

[angmor]

Correct me if im wrong, but the implications of Special Relativity only work in inertial frames of reference - this was to correct the Twin Paradox. therefore you cannot measure it from the frame of the electron since it isnt in an inertial frame - it has to be a rest frame so the answer is 0.1902m

 

[charismo]

haha it definitely had to be greater than the the length as observed by the electrons.. and im fairly certain its 0.3. haha whoever said something about the discharge tubes not moving near the speed of light ..wtf?? lol

 

[helper]

Correct me if im wrong, but the implications of Special Relativity only work in inertial frames of reference - this was to correct the Twin Paradox. therefore you cannot measure it from the frame of the electron since it isnt in an inertial frame - it has to be a rest frame so the answer is 0.1902m

After it passes the anode it is out of the electric field, so is no longer being accelerated, so can be assumed to be an inertial frame.

 

[mithu]

NOW EVERYONE. THE ANSWER IS 0.192 AND NOT 0.3. THE FRAME OF REFERENCE OF THE LABORATORY IS TAKEN TO BE THE STATIONARY FRAME AS THE QUESTION SPECIFIES THAT THAT IS THE FRAME FROM WHICH WE APPLY RELATIVITY. HENCE, BY LENGTH CONTRACTION, THE LENGTH OF THE ELECTRON IS LESS.

im with you yorky, shinji and glen.

ps. what did you guys get for the mass dilation question.

 

[Glen88]

I got approx. 1.14 x 10^-30kg, an increase in mass from 9.109 x 10^-31kg

 

[yankyfly]

NOW EVERYONE. THE ANSWER IS 0.192 AND NOT 0.3. THE FRAME OF REFERENCE OF THE LABORATORY IS TAKEN TO BE THE STATIONARY FRAME AS THE QUESTION SPECIFIES THAT THAT IS THE FRAME FROM WHICH WE APPLY RELATIVITY. HENCE, BY LENGTH CONTRACTION, THE LENGTH OF THE ELECTRON IS LESS.

im with you yorky, shinji and glen.

ps. what did you guys get for the mass dilation question.

ok... we are not measuring the length of the electron. We are measuring the a length which the electron observes. This length is not moving, which means the stationary labartory would not see it contract. So the answer is 0.3

I am 100% sure it is 0.3!! even if you just think about it empirically. 0.3 is a much cleaner answer than some shitty decimal 0.192. 0.192 is wrong under all circumstances

 

[Sober]

..

 

[XcarvengerX]

You guys saying that it is ANYTHING BUT 0.3 are off your chops. You are so wrong and have no idea what you are talking about. Despite being drunk I can say with the absolute certainty that your lack of ability to understand a concept that has been hammered into you for 12 months straight indicates your complete and utter flawed abililty to understand phsyics (or anything beyond the simple constructs that make life possible, food, enemy freind etc), before you argue back for the sake of argument or simply that you are so fucking arrogant: please double check with somebody with more sense than you that you are wrong. Go away, you started this exchange of distasteful words, you should bloody end it. Did you not read my explaination earlier?

Why would the board of studies offer multiple questions in a row that rely on the same train of thought anyway? If you seem to be finding alll the question easy then either you are extremely smart or your miscalculations are commmon to most. And based on your established error you are the latter.

Sorry if I offended you. I can't even remember who I'm arguing at (if anybody), that's what Beam does to you.

-out, not quirte so sober, (yeah some other blo joe made the pathetic joke but fuck, im gonna repeat it anyway)

Thanks Sober. At least you confirm that I got the mass one correct, and I think incorrect substitution in part (c) will only cost 1 mark. So stop arguing before you read the whole thread or otherwise just get over it.

Note: Physics is my "toy" subject anyway...

 

[angmor]

calm down dude we are here to discuss .... thats the whole point of a forum.

 

[P_Dilemma]

There's not much to discuss. It's either 0.3m or 0.1902m. Period.

Personally I rkn it's 0.3m

-P_D

 

[Angry.student]

i got 0.3m.

I figured when viewing from electron, distance would seem shorter, hence it meant that you would need to reverse the formular to get a longer distance.