PLEASE HELP: PHYSICS QUESTIONS

[KennyH]

Hey guys, in the second semester of college physics and need some help understand a problem I need to solve. Here it goes:

An electron in a television picture tube is accelerated through a potential difference of 10kV before it hits the screen. What is the kinetic energy of the electron in electron volts?

(a) 1.0 x 10 raised to the 4th eV
(b) 1.6 x 10 raised to the -15 eV
(c) 1.6 x 10 raised to the -22 eV
(d) 6.25 x 10 raised to the 22 eV


The correct answer is (a) I just can't seen to come up with that. I am sure it is quite simple, I think I am just overlooking something.

1eV = 1.60 x 10 raised to the -19 J


My question is how can I find kinetic energy when all the formulas use PE with the electron being accelerated?

 

[KennyH]

Can anyone help?

 

[Justin218]

Wish I could help ya, but only in high school physics, maybe in a few years Bump

 

[Heisenberg]

The answer is surprisingly simple. The potential difference of 10keV is the potential energy of the electron. Just before it hits the screen, all of the potential is converted into kinetic energy. The kinetic energy is then just 10keV.

 

[Heisenberg]

<< I would tend to accept an answer coming from a member whose username is Heisenberg.

Unless, of course, he is uncertain. >>



Thanks. I think you're the first person here to recognize the name.

 

[Schlocemus]

<<

<< I would tend to accept an answer coming from a member whose username is Heisenberg.

Unless, of course, he is uncertain. >>



Thanks. I think you're the first person here to recognize the name. >>



But if you know that answer with any precision what is it that you don't know with precision?

 

[KennyH]

Cool, my question is how do I convert 10kV = 10000V to electron volts(eV)? The only thing I have here that might help is 1eV = 1.60 x 10 raised to the -19J. Please help me understand this

 

[ShizNitz]

<< Thanks. I think you're the first person here to recognize the name. >>



Doesn't the mere act of reading a post by Heisenberg actually distort his original intentions?

 

[Haircut]

1 eV is defined as the energy acquired by an electron when accelerating through a p.d. of 1V

Therefore an electron accelerated by 10kV, i.e. 10000V acquires an energy of 10000 eV.
The actual value of an electron volt does not matter for this question.

Hope this helps you a bit.

 

[jeremy806]

Dude,

Volts is J/C. Take the path integral of the charge moving through the potential (q dV) to determine the energy transferred.

(It takes 10kJ to move 1 C through a 10kV potential.)

Make sense?

Jeremy

 

[Heisenberg]

<< Cool, my question is how do I convert 10kV = 10000V to electron volts(eV)? The only thing I have here that might help is 1eV = 1.60 x 10 raised to the -19J. Please help me understand this >>



An electron volt is just the potential energy of one electron in a one volt potential. If you have one electron in 10,000 V, you have a PE = 1 electron * 10,000 V = 10,000 eV. It's not neccessary to convert to Joules. Again, since all of the potential energy gets converted to kinetic just before the electron hits the screen, the kinetic energy is 10keV.

 

[RaynorWolfcastle]

In joules, Potential Energy (PE) = charge (q) * Difference of Potential (V)

so PE = qV
1eV = 1.60 x 10^(-19) J

to get an answer in eV divide both sides by 1.6 x 10^(-19)
but...the charge of an electron in coulombs = 1.6 x 10^-19

therefore

PE (in eV) = V

therefore for a 10 kV potential difference, the electron will have a KE of 10 eV

In which deltaX x deltaP = h-cross , right Heisengerg?

-Ice

 

[VinayN]

PE = qV
PE = -KE
-KE = qV
since it is an electron, q = -1.6*10^-19
KE=+1.6*10^-19 * (1*10^4) V
since it needs to be measure in electron volts(eV) divide by 1.6 * 10^-19
KE = 1 * 10^4 eV

I am in 9th grade and failing this XD

 

[Red Squirrel]

All those calculations aside, at the end of the day, the plane takes off.

 

[BoomerD]

PE = qV
PE = -KE
-KE = qV
since it is an electron, q = -1.6*10^-19
KE=+1.6*10^-19 * (1*10^4) V
since it needs to be measure in electron volts(eV) divide by 1.6 * 10^-19
KE = 1 * 10^4 eV

I am in 9th grade and failing this XD

And you're not smart enough to realize this thread is about 19 years old...the OP possibly graduated college by now...and...DO YOUR OWN HOMEWORK!

 

[SKORPI0]

All those calculations aside, at the end of the day, the plane takes off.

I wonder why airports don't use conveyour belts/treadmills instead of those long landing strip.

 

[snoopy7548]

I'm so glad I'm an electrical engineer - we use math which the physicists already figured out and dumbed down for us, and we make more money.

 

[shortylickens]

PE = qV
PE = -KE
-KE = qV
since it is an electron, q = -1.6*10^-19
KE=+1.6*10^-19 * (1*10^4) V
since it needs to be measure in electron volts(eV) divide by 1.6 * 10^-19
KE = 1 * 10^4 eV

I am in 9th grade and failing this XD

Dude,

the OP needed an answer NINETEEN YEARS AGO!

He already graduated college, got a sweet gig at Intel, retired, and bought a house on Puget Sound.

 

[dank69]

Dude,

the OP needed an answer NINETEEN YEARS AGO!

He already graduated college, got a sweet gig at Intel, retired, and bought a house on Puget Sound.

How do you know he isn't still sitting at his desk waiting for an answer?

 

[spacejamz]

How do you know he isn't still sitting at his desk waiting for an answer?

he is probably still filling out his TPS reports...

 

[Stopsignhank]

The answer is 0 (zero). TVs do not have picture tubes these days.