Electric Potential/Electric Potential Energy question

In summary, the conversation discusses a problem involving the transfer of electrons from a hand to a metal door knob. The electric potential of the knob is 2.0 X 10^4 V greater than that of the hand and the work done by the electric force on the electrons is 1.5 X 10^-7 J. The question asks for the number of electrons that jump from the hand to the knob, and the conversation goes into detail about how to solve the problem, with an emphasis on being careful with units in calculations.
  • #1
benji
48
0
We just started this stuff in my AP Physics class and I'm not catching on to it too quickly... At least problem solving-wise. I thought I had all the concepts down, but maybe not.

Here's a question I'm having problems with:

Just as you touch a metal door knob, a spark of electricity (electrons) jumps from you hand to the knob. The electric potential of the knob is 2.0 X 10^4 V greater than that of your hand. The work done by the electric force on the electrons is 1.5 X 10^-7 J. How many electrons jump from your hand to the knob?

How do I go about this one? I'm sure it's a pretty simple problem because it's at the beginning of the chapter, but I guess I'm missing a connection or something.
 
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  • #2
well, voltage is potential energy per charge, and the charge on a single electron is -1.6*10^-19 couloumbs.
 
  • #3
I see, so what I did was:

1.5 X 10^-7 / -1.6 X 10^-19 = -9.375 X 10^11 electrons
-9.375 X 10^11 / 2 = 4.68 X 10^11 elections

So 4.68 X 10^11 electrons was very close to the correct answer. Did I do this right?
 
  • #4
Your work is a little sketchy. First of all, Joules/charge does not have units of "electrons", and I don't know what a negative number of electrons means. I get the idea of what you're doing, but you should be a lot more careful with units. Then, you seem to have forgotten the power of ten on the voltage.
 

What is electric potential?

Electric potential is a measure of the potential energy of a charged object in an electric field. It is the amount of work needed to move a unit positive charge from a reference point to a specific point in the electric field.

How is electric potential different from electric potential energy?

Electric potential is a measure of the potential energy per unit charge, while electric potential energy is the total potential energy of a charged object in an electric field. Electric potential is a scalar quantity, while electric potential energy is a vector quantity.

What is the formula for calculating electric potential?

The formula for electric potential is V = kQ/r, where V is the electric potential, k is the Coulomb's constant, Q is the charge of the object, and r is the distance from the object to the reference point.

How does electric potential change with distance from a charged object?

As the distance from a charged object increases, the electric potential decreases. This is because the electric field strength decreases with distance, and electric potential is directly proportional to electric field strength.

Can electric potential be negative?

Yes, electric potential can be negative. This occurs when the reference point is chosen to be at a higher potential than the point being measured. It simply means that a positive charge would have a lower potential energy at that point.

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