# Help equation to find # of electrons

• Charles C
In summary, when you touch a metal door knob, a spark of electricity jumps from your hand to the knob. The electric potential difference between your hand and the knob is 2.0*10^4 V, and the work done by the electric force on the electrons is 1.5*10^-7 J. Using the equation W = qΔV and the charge of 1 electron, we can calculate that 4.7*10^7 electrons jump from your hand to the knob.
Charles C
[SOLVED] Help equation to find # of electrons

## Homework Statement

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

## Homework Equations

-W/Va-Vb=C
1e = 1.6*10^-19 Coulombs

## The Attempt at a Solution

1.5E-7 / 2E4 = 7.5E-12
7.5E-12 / 1.6E-19 = 4.7E7 Electrons.

Last edited:

Hello,

Based on the given information, we can use the equation W = qΔV to calculate the number of electrons that jump from your hand to the knob.

W = 1.5*10^-7 J
ΔV = 2.0*10^4 V
q = number of electrons

Substituting in the values, we get:

1.5*10^-7 J = q * 2.0*10^4 V

Solving for q, we get:

q = 1.5*10^-7 / 2.0*10^4 = 7.5*10^-12

Since we know that 1 electron has a charge of 1.6*10^-19 C, we can convert the charge to the number of electrons:

7.5*10^-12 C / 1.6*10^-19 C = 4.7*10^7 electrons

Therefore, 4.7*10^7 electrons jump from your hand to the knob when you touch the metal door knob.

Great job on solving the problem! To explain the solution, we can use the equation W = qΔV, where W is the work done, q is the charge (in Coulombs) and ΔV is the change in electric potential (in Volts). We know the values for W and ΔV, so we can rearrange the equation to solve for q, which represents the number of electrons in this case. This is where you got your first step of 1.5E-7 / 2E4 = 7.5E-12.

However, we need to convert this value to Coulombs, which is the unit for charge. This is where the second equation comes in, where 1e (electron charge) is equal to 1.6*10^-19 Coulombs. So we divide 7.5E-12 by 1.6E-19 to get the final answer of 4.7E7 electrons. This means that 4.7E7 electrons jumped from your hand to the knob when you touched it. Great work!

## 1. How do I use the equation to find the number of electrons in an atom?

To use the equation, you need to know the atomic number of the element and the charge of the atom. The atomic number represents the number of protons in the nucleus, which is equal to the number of electrons in a neutral atom. The charge of the atom can be positive or negative, indicating an imbalance of protons and electrons. Once you have these values, you can use the equation Number of Electrons = Atomic Number - Charge to find the number of electrons.

## 2. What is the atomic number and how is it related to the number of electrons?

The atomic number is the number of protons in the nucleus of an atom. Since atoms are electrically neutral, the number of protons is equal to the number of electrons. Therefore, the atomic number also represents the number of electrons in a neutral atom.

## 3. Can the equation be used to find the number of electrons in an ion?

Yes, the equation can be used to find the number of electrons in an ion. In this case, the charge of the ion must be taken into account. The charge can be positive or negative, indicating an excess or deficiency of electrons. By using the equation Number of Electrons = Atomic Number - Charge, you can determine the number of electrons in an ion.

## 4. Is the equation valid for all elements?

Yes, the equation can be used for all elements. The atomic number is a unique identifier for each element, and the charge can be positive or negative for any element. Therefore, the equation can be applied to any element to find the number of electrons.

## 5. How do I know if I have calculated the correct number of electrons using the equation?

You can check your calculation by making sure that the number of electrons you have calculated is equal to the atomic number minus the charge. Additionally, you can compare your result to the number of electrons listed on the periodic table for that element. If your calculated number matches the listed number, then you have found the correct number of electrons.

• Introductory Physics Homework Help
Replies
3
Views
2K
• Introductory Physics Homework Help
Replies
6
Views
869
• Introductory Physics Homework Help
Replies
20
Views
3K
• Introductory Physics Homework Help
Replies
3
Views
8K
• Introductory Physics Homework Help
Replies
34
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
2K
• Introductory Physics Homework Help
Replies
2
Views
8K
• Introductory Physics Homework Help
Replies
5
Views
2K
• Introductory Physics Homework Help
Replies
3
Views
1K
• Introductory Physics Homework Help
Replies
14
Views
2K