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.
Wouldn't you need more information?
I thought about writing just under the speed of light but there is another quesiron like this.
Thanks
Ian
0
Quick Quesiton
Started by Ian, Nov 13 2005 08:22 PM
8 replies to this topic
#2
-
- Moderators
-
- 1,497 posts
Fully Fledged Genius
- Location:Cambridge (Term Time), Bearsden (Glasgow) Non Term Time
- Gender:Male
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.
![\[
\begin{array}{l}
QV = \frac{1}{2}mv^2 \\
v = \sqrt {\frac{{2QV}}{m}} \\
v = \sqrt {\frac{{2 \times \left( {1.6 \times 10^{ - 19} } \right) \times \left( {7.5 \times 10^5 } \right)}}{{9.11 \times 10^{ - 31} }}} \\
\end{array}
\]](/latexrender/pictures/3f3a17fd91a1794bf94c6577e106c7f4.gif "\[
\begin{array}{l}
QV = \frac{1}{2}mv^2 \\
v = \sqrt {\frac{{2QV}}{m}} \\
v = \sqrt {\frac{{2 \times \left( {1.6 \times 10^{ - 19} } \right) \times \left( {7.5 \times 10^5 } \right)}}{{9.11 \times 10^{ - 31} }}} \\
\end{array}
\]")
Click here to visit the Bearsden Academy Website
If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!
If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!
#3
-
- Members
-
- 52 posts
Good Effort
- Gender:Male
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
#4
-
- Members
-
- 1,955 posts
Fully Fledged Genius
- Gender:Male
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.
, the accelerating force IS the electric field due to the potential difference, me thinks.
#5
-
- Moderators
-
- 1,497 posts
Fully Fledged Genius
- Location:Cambridge (Term Time), Bearsden (Glasgow) Non Term Time
- Gender:Male
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.
That's why I'm suggesting that either you need to consider relativistic effects or I have done something stupid.
Click here to visit the Bearsden Academy Website
If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!
If you can keep your head when all about you
Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!
#6
-
- Members
-
- 52 posts
Good Effort
- Gender:Male
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?
#7
-
- Moderators
-
- 4,252 posts
Ruler (but not owner) of hsn
- Location:kilmarnock(ok kilmaurs)
- Interests:programming, exercising, brass band, using this board
- Gender:Male
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
although i think most time i got that it was due to a stupid mistake
If i am not here i am somewhere else
#8
-
- Members
-
- 95 posts
Good Effort
- Gender:Male
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.
Nothing!!!!!!!!
#9
-
- Admin
-
- 720 posts
Child Prodigy
- Location:West Lothian
- Gender:Male
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
1 user(s) are reading this topic
0 members, 1 guests, 0 anonymous users
