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## Homework Statement

Can the cutoff potential (v) be the same as kinetic energy measured in electron volts

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- Thread starter garr6120
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- #1

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Can the cutoff potential (v) be the same as kinetic energy measured in electron volts

- #2

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No. electron-volt is a unit of energy; volt is energy only when multiplird by charge.

- #3

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in my class we are doing this physics lab where we get the data, so i have used the equation KE=qV where q is 1.60*10^-19 C which is the charge on an electron, and V is the current at the cutoff potential. So for yellow light i have the values 0.25 J/C. Now I got an answer of 4.0*10^18 J when solving the equation. However, the question also says write your answer in electron volts, I know that one eV is 1.60*10^-19 J/eV, same value as the charge on an electron but different units. anyways i divided 4.0*10^18 J by 1.60*10^-19 J/eV and i got 0.25 eV same as what i had before. I am so confused. This screenshot might make better sense.

- #4

- 7,881

- 798

You have the charge of the electron wrong. It's 1.6e-19C, not 1.6e19C.

"

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Oh?

Your statement is very confusing on top of that. Try to frame your question precisely. What is it you're solving for?

- #5

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Is it possible to get a negative KE value?

- #6

- 7,881

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So you have an initial k.e. of 0.25 ev but the electrons LOSE energy as they move to the plate. That energy is qV with q negative and V negative.

Don't just depend on equations to give you the right polarity in any given problem. Think it through.

And no, there is no such thing as negative kinetic energy. k.e. = 1/2 mv

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