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OCR Physics B Synoptic: Beta faster than speed of light?! Help!

Hi, this is from the OCR Physics B synoptic article on neutrino's...

"Some beta particles have an energy of 1.16Mev"

However, if you convert this into velocity, using:

m=9.11*10^-31

v = (2E/m)^1/2

Velocity = 6.3*10^8 m/s

Someone please work out why this is greater than the speed of light, if I don't figure it out it's bound to come up on the exam!

Thanks (and some rep) if you can help, tom

Reply 1

elpaw

you cant use E = mv²/2 relativistically

you have to use E = γmc², where γ = 1/√(1-v²/c²)

Reply 2

currency_westlake

elpaw

you cant use E = mv²/2 relativistically

you have to use E = γmc², where γ = 1/√(1-v²/c²)

I've come across that formula before but it's not part of the A-Level syllabus. Furthermore, the 1/2mv^2 formula has often been used in the past with radiation energies.

Thanks anyway, at least I know my calculation isn't wrong!...

Reply 3

Indelible

Ive spent 30 minutes trying to figure this git out. For the first 5 minutes I forgot to convert to J :mad:

gota watch out for that in the exam! quite frankly I dont know, and dont understand :frown:

Reply 4

bhp

the beta particle may have enough energy to theoretically travel at speed of light but as the speed approaches speed of light the mass of the particle actually increases and therefore gains more drag and this keeps it from reaching the elusive speed of light. i don't actually understand how objects gain mass as the go faster and gain energy but the equation:

change in energy = change in mass x speed of light^2

Reply 5

fred86

hey, u done that sheet of questions that's been previously posted, anyone feeling like contributing answers?
Fred

Reply 6

elpaw

using my earlier formula, i get the answer as the beta particle travelling at 89.6% of the speed of light.

Reply 7

Text_Box

elpaw

using my earlier formula, i get the answer as the beta particle travelling at 89.6% of the speed of light.

Problem is, that formula wasn't on the A-Level syllabus. Maybe their answer would be acceptable in terms of getting the marks? :confused:

Reply 8

elpaw

Text_Box

Problem is, that formula wasn't on the A-Level syllabus. Maybe their answer would be acceptable in terms of getting the marks? :confused:

i just dont think they would ask the question. or if they did, they would say "assuming you can use the classical form of kinetic energy, what should the particle's speed be?" or words to that effect

Reply 9

currency_westlake

Despite the fact that we haven't reached a conclusion, I would like to thank all of you for showing me that I hadn't gone mad and done something wrong!

Tom

Reply 10

Rose in Bloom

tomhitchings

Hi, this is from the OCR Physics B synoptic article on neutrino's...

"Some beta particles have an <a href="http://www.ntsearch.com/search.php?q=energy&v=56">energy</a> of 1.16Mev"

However, if you convert this into velocity, using:

m=9.11*10^-31

v = (2E/m)^1/2

Velocity = 6.3*10^8 m/s

Someone please work out why this is greater than the speed of light, if I don't figure it out it's bound to come up on the exam!

Thanks (and some rep) if you can help, tom

I think I might be able to help here....as an accelerated particle approaches the speed of light, its mass increases significantly and a slight rise in v...beacuse nothing can travel faster than light therefore this happens as the particle APPROACHES c, not before that, before that the speed increases as you'd expect it to!

Reply 11

Turbonutter

The particles gain mass because their mass is defined by their energies, and as their speed closes in on the speed of light, this kinetic energy starts to make a difference.

Reply 12

dreamer

Where is this sheet fred?

Maybe it is the one I have been given by teachers.

I was wondering, can anyone explain the logic behind the last bit: Why is having more distance going to mean fewer electron-neutrinos? Surely if it's oscillating, it's gonna be able to oscillate back and forward just as much with the greater distance and the net effect will be zero??

Reply 13

zizou

yeah
in line 121, it says, if neutrino have mass,however, there is a possible explanation for solar neutrino problem - nuetrinos with mass can theoretically 'oscillate' or change between generations, from electron-neutrino to tau-neutrino.

therefor most distance travelled by the electron-neutrino will mean that there is more chance for these to collide with other particle and annihilate to increas there mass, therfore they change generation from electron-nuetrino to tau-nuetrino, thus it will mean less electron-neutrino.....i hope its right.....ne one got ne other suggestions?