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garr6120
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Homework Statement
Can the cutoff potential (v) be the same as kinetic energy measured in electron volts
Cutoff Potential vs. Kinetic Energy in Electron Volts: What's the Difference?
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In summary, the conversation discusses the relationship between cutoff potential and kinetic energy measured in electron volts. The student is attempting to solve a physics lab question using the equation KE=qV, where q is the charge on an electron and V is the cutoff potential. However, there are some errors in the student's understanding, such as the incorrect charge of an electron and confusion between current and cutoff potential. The conversation also addresses the possibility of negative kinetic energy and the importance of understanding the concepts behind formulas.
Can the cutoff potential (v) be the same as kinetic energy measured in electron volts
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No. electron-volt is a unit of energy; volt is energy only when multiplird by charge.
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garr6120
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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.
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"Now I got an answer of 4.0*10^18 J when solving the equation."
You have the charge of the electron wrong. It's 1.6e-19C, not 1.6e19C.
"V is the current at the cutoff potential.". No, V is the cutoff potential.
"i divided 4.0*10^18 J by 1.60*10^-19 J/eV and i got 0.25 eV.
Oh?
Your statement is very confusing on top of that. Try to frame your question precisely. What is it you're solving for?
You have the charge of the electron wrong. It's 1.6e-19C, not 1.6e19C.
"V is the current at the cutoff potential.". No, V is the cutoff potential.
"i divided 4.0*10^18 J by 1.60*10^-19 J/eV and i got 0.25 eV.
Oh?
Your statement is very confusing on top of that. Try to frame your question precisely. What is it you're solving for?
- #5
garr6120
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I have made all of my corrections to the charge of an electron and the amount of joules in an electron volt. Now i am trying to solve for the max KE of the electron using the equation KE=qV, where q is the charge on an electron: -1.60*10^-19 C, and V is the cutoff potential when the current is 0. Using this information for green light which has a cutoff potential of 0.25 V. I can now solve for the maximum KE possible, when i do this i get an answer of -4.0*10^-20 J. This question also wants me to convert J to electron volts, since i know that one electron volt is 1.60*10^-19 J/eV, i divided -4.0*10^-20 J by 1.60*10^-19 J/eV to get an answer of -0.25 eV.
Is it possible to get a negative KE value?
Is it possible to get a negative KE value?
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Instead of just using formulas, try to see what you're really doing. You're firing electrons with an initial k.e. of 0.25 ev at a NEGATIVE plate. So what happens? As you inrease the voltage NEGATIVELY, higher and higher REPULSIVE force is applied to the speeding electrons until the voltage is negative enough to apply just enough repulsive force to prevent the electrons from arriving at the plate. They instead do a 180 in front of the plate and head back to the emitter.
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 mv2 so even if v is negative, k.e. is positive.
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 mv2 so even if v is negative, k.e. is positive.
FAQ: Cutoff Potential vs. Kinetic Energy in Electron Volts: What's the Difference?
1. What is cutoff potential?
Cutoff potential refers to the minimum voltage required to stop the flow of electrons in a circuit. It is usually measured in volts and is used to regulate the flow of current in electronic devices.
2. How is cutoff potential determined?
Cutoff potential is determined by the material and design of the circuit or electronic device. It can also be adjusted by changing the voltage or resistance in the circuit.
3. Why is cutoff potential important in electronics?
Cutoff potential is important because it helps regulate the flow of current in electronic devices. It also helps prevent the device from overheating or becoming damaged due to too much current.
4. Can the cutoff potential be changed?
Yes, the cutoff potential can be changed by adjusting the voltage or resistance in the circuit. It can also be changed by using a different material or design for the circuit or electronic device.
5. How does cutoff potential affect the performance of an electronic device?
Cutoff potential can greatly affect the performance of an electronic device. If the cutoff potential is too low, the device may not function properly or may overheat. If it is too high, the device may not have enough power to function. Finding the optimal cutoff potential is important for the proper functioning of electronic devices.