## Quick Quesiton

### Ian

Posted 13 November 2005 - 08:22 PM

Can someone pelase help with this problem?

Electrons are accelerated through a large potential difference of 7.5x10^5V. The electronas are initially at rest. Calculate the speed reached by these electrons.

I thought about writing just under the speed of light but there is another quesiron like this.

Thanks

Ian

### werlop

Posted 13 November 2005 - 08:50 PM

OK, I am remembering the constants from memory from several months ago, so correct them if they are wrong. Also, the final answer to this is very high so either I have done something silly or you will need to consider relativistic effects.

### Ian

Posted 13 November 2005 - 09:11 PM

Why i there a maximum energy the electron can reach? Why would it not accelerate from the speed you calculated

### dfx

Posted 13 November 2005 - 10:04 PM

Well according to your equation QV = 1/2mv , the accelerating force IS the electric field due to the potential difference, me thinks.

### werlop

Posted 13 November 2005 - 10:06 PM

Well from what I did the electron would end up faster than c and obviously that isn't going to happen, as as v tends to c, m tends to infinity, etc.

That's why I'm suggesting that either you need to consider relativistic effects or I have done something stupid.

### Ian

Posted 13 November 2005 - 10:15 PM

But why does the potential difference matter? if it was 1V of 1,000,000V wouldn't it never reach a maximum speed. Wouldn't it jsut get getting closers to C?

### Dave

Posted 13 November 2005 - 10:31 PM

yeah if i remember right didnt we just say that although that was the value found from calculation this would never be the case becase v cannot be greater than c

although i think most time i got that it was due to a stupid mistake

### Jason Bourne

Posted 19 January 2006 - 03:25 PM

[right][/right]
[/quote]

Where did you get these math graphics from that i cant find anywhere how to properly make.

### George

Posted 19 January 2006 - 05:03 PM

QUOTE(Jason Bourne @ Jan 19 2006, 03:25 PM)
Where did you get these math graphics from that i cant find anywhere how to properly make.

I posted a quick introduction here: http://www.hsn.uk.net/forum/index.php?show...indpost&p=65413