IIT JEE , AIEEE Forum - Physics , Optics

ashgirl

arrang in increasing order of magnitude:

escape velocity of electron frm earth's gravity, velocity of free electron in earths atmosphere at room temp, velocity of light, typical drift velocity of electron in metal.

ashgirl

c'mon yaar!!!! cant anybody answer dis for me plz?????

ramyani

typical drift velocity of electron in metal is lowest and velocity of light is highest. The rest I m not sure.

shubham_sachdeva

vel. of light>escape vel>drift vel>vel of e in free atm...it came in our school exam....:)

ashgirl

i thought drift velocity was the least!!!!!

?????

shubham_sachdeva

drift velocity is few mm/sec but vel. in atmosphere is in cm/sec....i read it sumwhere..

rooney

typical drift vel. of e- in metal < velocity of free electron in earths atmosphere at room temp < escape velocity of electron frm earth's gravity < velocity of light

ashgirl

now i am getting confused!!!!

shubham_sachdeva

rooney i am confirmed yaar......this qn. came in our skool exam & i got full marks here....

rooney

@shubham

You urself said that "drift velocity is few mm/sec but vel. in atmosphere is in cm/sec....i read it sumwhere..". So, drift velcotiy <<<<< vel in atmosphere. But in your answer you are saying the opposite thing.

Drift vel is around 0.1 mm/sec. Speed of e- in atmosphere less than this ? Impossible.

harsha_27

as a metal is denser than atmosphere,so more collisions will be there in the metal than in the atmosphere and also because the forces acting in a metal are electrostatic forces and intermolecular forces but in atmosphere there is only weak vanderwaal attraction ......so the velocity will be more in the air than in the metal...and coming to escape velocity,firstly there is no significant gravitational force acting on the electron and also no significant gravitational potential energy,so to be escaped out of the earth it may do two things 1. collide with a molecule 2. penetrate into a molecule and come out............so it has to overcome the energy lost during the collision with the molecules it encounters moreover size of electron is so small that it can easily penetrate through the molecule .......if that happens electrostatic forces b/w the nucleus of that atom also acts on this electron so in order to escape off from that high retarding forces the electron must possess very very high velocity ....so in order to over come 1000 s of such molecules think of the velocity it must possess .....in fact it may be greater than velocity of light...even if it is not its velocity may be at least comparable with the velocity of light and we know that from Einstien's mass energy relation ...........with near light velocity electrons mass is converted into energy and it vanishes....so practically it is impossible to throw an electron out of the earth so i think the order may be escape velocity of electron frm earth's gravity>velocity of light>velocity of free electron in earths atmosphere at room temp>typical drift velocity of electron in metal........see this is only my prediction ........so it may or may not be correct if u r convinced with this explanation then o.k. otherwise leave it....lets wait for an expert's answer

shubham_sachdeva

sorry sorry i mean drift vel. is in mm/sec & vel. of electron in earth's atmosphere is in micro or maybe 10^-5 m/sec.....u wanna say dat our skool teachers are wrong.....i agree wid u to sum extent ;) but not to dis level dear......

@harsha. anything cann;t have speed more than vel. of light......as it can be seen from the foll/ relation..

m = rest mass/(1 - (v/c)^2)^1/2 acc. to u v>c so denominator becomes imaginary & dats impossible.....hope u got it!!!!

rooney

@Shubham

Well...Yes. I would not believe Einstein himself if there is no logic behind what he says. Give proof or it didnt happen.

shubham_sachdeva

i don't know the reason but true is true.............well what i can guess is dis that drift vel. is i think vel. acquired by electrons when a potential is applied....so in this case all electrons must be flowing in same direction hence no collision b/w them while in second case there is no potential applied .so eletrons must be moving in random directions....hence more no. of collisions....so less speed........dats what i thought...........what u think u tell(Einstein).....

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