Kinetic energy in electron volts

[LuigiAM]

Homework Statement

How much kinetic energy is in electron volts?

Homework Equations

Kinetic energy = 1/2 mv²
1 electron volt = 1.6 x 10^-19 J

The Attempt at a Solution

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It's a bit unclear to me what the question is asking, since no context at all is given. It's one of the questions in the homework and it's a separate question from the others so it's not part of a bigger problem.

Since kinetic energy is in joules and there is 1.6 x 10^-19 Joules in one electron volt, I just put that as the answer, but I feel like I'm missing something? Maybe they're just trying to make us look up the value of an electron volt?

 

[Orodruin]

The kinetic energy of what? Electron volts is just a unit of energy.

 

[kuruman]

It is unclear to me too what the question is asking. It is a poorly phrased question. It's like asking how much horizontal distance is in miles?

 

[LuigiAM]

Hmm I'm glad I'm not the only one who doesn't get it. I'm going to try to email the teacher and ask him if there was a mistake in the question. It doesn't seem to be related to another question since the question before it is about equivalent resistance in a circuit and the one after is about the potential difference between two points. It's possible that he forgot to include a diagram or something.

 

[LuigiAM]

Homework solutions were just posted this morning. The correct answer was "The electron volt is the energy acquired by an electron in moving through a potential difference of one volt."

I should've suspected that this is what he was asking for because it's the definition he gave us in class. I didn't think about it at all. I think I was just thrown off by the word "kinetic energy" in the question

 

[Orodruin]

To be honest, if the wording of the problem was as you have stated it here, then the problem lies with your teacher not being able to properly formulate himself. What he is asking for is the definition of the unit electron volt, not the kinetic energy of something in electronvolts.

When confronted with bad formulations you should ask for clarification. If you do not get it, you should complain.

What was the exact question word for word?

 

[kuruman]

Thank you for posting the answer for our edification. It is a poorly phrased question. Note that the answer says nothing about kinetic energy. If I were to grab an electron and move it at constant speed through a potential difference of one volt, the electron would acquire an electron volt's worth of potential energy. Perhaps a better way to ask the question would be, "What must happen for an electron to change its kinetic energy by one electron volt?" to which the answer would be, "the electron must move through a potential difference of one volt."

 

[LuigiAM]

Thanks for the replies. Yes, I re-copied the question word for word.

Anyway I think the difficulty with this class is the language barrier. Our professor has a PhD in physics and worked as a theoretical physicist so he obviously knows the material. The problem is that his english is very poor. It usually isn't that big of a problem because it's often clear what he means. Like, when he says "calculate gravity of moon" it's obvious that he means "calculate the gravity on the moon" even if he doesn't use particles. But sometimes the meaning of the question is obscured, unfortunately.