Length contraction??? (1 Viewer)

[angmor]

ok for the length question. Lv was the length they gave you right? they wanted you to find Lo ?

 

[shinji]

dude ur overthinking it, it contracts, but only observers in different frame of reference can see contraction

yeah,,and i shall quote the question.

Calculate this distance as measured in the laboratory frame of reference

hence, greater distance is measured~?

 

[yorky]

the laboratory frame of reference is the different frame of reference mate, it is stationary, therefor the contrraction is seen, read lizcat, if u dont understand give up

 

[shinji]

hey, u know what i say?

Fuck relativity!
fuck it and it's mind bogglign shit >_<
nyahh, but do you still see where i'm coming from though?

 

[psychopath]

i dunno yorky man .. i put .19 as well .. cos that's what i think it is .. but then i guess what they're saying makes sense .. cos it's the electron moving .. not the tube .. if it was the tube moving .. then the tube woud shrink .. and hence the distance would shrink .. but since the electron is moving .. it's the electron that will shrink .. not the distance it has to travel .. if anything .. the distance is the same .. OMG IT'S THE SAME! maybe .. ahahah who knows .. but yeh i'm inclined to believe it's 0.3 .. cos you know how in space travel .. the distance that the astronauts see themselves travelling is much shorter and they do it in a faster time .. so isnt it the same for th eelectron? cos just ignore the tube.. just pretend it's moving from point A to point B .. if it's going super fast .. the distance will contract .. and it will measure it as .24 .. but at rest it measures it at .3 ..

my main problem now with the question is that the question clearly states the elcetron starts at restfrom the cathode .. so doesnt that mean that the electron coulda measured the distance from rest as well as while moving??? i dunno .. i hope i just lose one mark cos i at least got the equation and stuff right ..

 

[Glen88]

Alright, it's time for me to settle this.

The distance between the anode and the screen, as measured in the electron's
frame of referencei,s 0.24 m.
Calculate this distance as measured in the laboratory frame of reference.

The electron, having contracted will view the distance between the anode and screen as having increased relative to itself. The external frame of reference is anything other than the electron itself. Thus, 0.24m as witnessed by the electron, IS the increased value. Therefore, 0.24m being the increased length, is larger than the observed length in the lab, which is approx 0.19m.

 

[shinji]

i dunno yorky man .. i put .19 as well .. cos that's what i think it is .. but then i guess what they're saying makes sense .. cos it's the electron moving .. not the tube .. if it was the tube moving .. then the tube woud shrink .. and hence the distance would shrink .. but since the electron is moving .. it's the electron that will shrink .. not the distance it has to travel .. if anything .. the distance is the same .. OMG IT'S THE SAME! maybe .. ahahah who knows .. but yeh i'm inclined to believe it's 0.3 .. cos you know how in space travel .. the distance that the astronauts see themselves travelling is much shorter and they do it in a faster time .. so isnt it the same for th eelectron? cos just ignore the tube.. just pretend it's moving from point A to point B .. if it's going super fast .. the distance will contract .. and it will measure it as .24 .. but at rest it measures it at .3 ..

my main problem now with the question is that the question clearly states the elcetron starts at restfrom the cathode .. so doesnt that mean that the electron coulda measured the distance from rest as well as while moving??? i dunno .. i hope i just lose one mark cos i at least got the equation and stuff right ..

lol yeah.

that's what i did! ~~
and i endorse what i said earlier:
"Fuck relativity" =]

also, the wording of the question. maybe they didn't require you to think tht hard? maybe it was bad wording question tht was a simple application of length contraction. coz i rekkon if u had to manipulate it around, they'd issue 3 marks to tht question?

 

[Lizcat]

someone should just ask their physics teacher, bags not me! hehe
its a really confusing Q.

 

[doraemon]

the electron is travelling in its inertial frame. the world around him is moving at 0.6c

if the contracted length of the world around him is 0.24m, that makes his distance 0.3m

 

[rolfey24]

man glen ur a tool.u frigen hitler. it was 0.18.

 

[Glen88]

Think of a train, if the electron was the train having itself contracted as it is an object travelling at relativistic speeds, when it looks out the window at the distance it is travelling, it would detect that the outside world or its track, has become longer, 0.24m. Therefore, we see it as being smaller than 0.24. Therefore = 0.19m.

Something tells me i'll be explaining this again.

 

[4DOGS]

Its a simple length contraction question. you sub in the rest length and the relative speed and that de dar the length contracts to .19m

some people just hav 2 live with in that they lost 2 marks here.

 

[shinji]

Think of a train, if the electron was the train having itself contracted as it is an object travelling at relativistic speeds, when it looks out the window at the distance it is travelling, it would detect that the outside world or its track, has become longer, 0.24m. Therefore, we see it as being smaller than 0.24. Therefore = 0.19m.

Something tells me i'll be explaining this again.

im currently not caring nemore.

haha .. my brain is fried from all the freaking relativity thinking.
BAH!
*/kill*

 

[Glen88]

man glen ur a tool.u frigen hitler. it was 0.18.

How about I contract your head Jared. Btw your closer than these 0.3 guys.

 

[angmor]

I GOT 0.1902m. the question said in the frame of the labotary. which is the inertial resting frame. therefore in your equation the value for the eletron is Lv...they want you to fidn Lo the initial rest mass in the laboratory frame

 

[doraemon]

it would detect that the outside world or its track, has become longer.

becoming longer? its length contraction.

 

[Glen88]

The...electron...is...contracting.


Therefore, the anything external to the electron, relative to the electron, appears to be longer. The only thing contracting is the electron. It is the thing travelling at relativistic speeds.

 

[vnblueberry]

put it this way
IF IT IS FROM PARTICLES PERSPECTIVE THE ANSWER IS 0.3
IF IT IS FROM THE LABS PERSPECTIVE THE ANSWER IS 0.19 BLABLABLABA
from MY memory (which WELL could be wrong) i read it as particles perspective, hence 0.3.

i cannot remember EXACTLY what the question said
now unless one of you stuffed that question up, asked for another sheet for that question, and kept it whilst on the way out and can take a picture OR scan it ONLINE, we will never know what it said. our memory plays tricks on us and will make us BELIEVE we read what we read, only hard evidence will do for me.

end of story

 

[Glen88]

Exactly from the exam:

The distance between the anode and the screen, as measured in the electron's
frame of reference is 0.24 m.
Calculate this distance as measured in the laboratory frame of reference.

Accept it...I'm just...right.

 

[helper]

Question
In a special investigation, the voltage between the cathode and the anode is increased so that an electron gains a velocity of 0.60 c, where c is the speed of light. The electron starts from rest at the cathode.

Calculate the mass of this electron in the laboratory frame of reference.

The distance between the anode and the screen, as measured in the electron's frame of reference, is 0.24 m.

Answer
Assuming uniform velocity, because we only use special relativity formulas

Electron and Plates are in different frames of reference. The plates are moving from the view of the electron. So the distance measured by the electron is L_v The electron observes it as it has contracted.

Calculating L_o, you are measuring the length an observer that is stationary with respect to the plates. This is the laboratory so L_o is the length you were asked to calculate.