Damn units and surface charge density.

In summary, The question asks to find the surface charge density on a large, flat sheet of charge based on the repulsive force of 2.1×10^−12 N experienced by an electron near the sheet. Using the formula F = qe with 2.1e-12 for the force and 6.1e-19 for the charge of an electron, the resulting E-field value was used in the formula E = (surface charge density)/2epsilon_0, with epsilon_0 being 8.85e-12. This calculation yielded a value of 2.32e-42 C/m^2, but it was deemed incorrect. Further calculations showed that there may have been an error in the
  • #1
frasifrasi
276
0
Ok, the question asks:

An electron close to a large, flat sheet of charge is repelled from the sheet with a 2.1×10^−12 {N} force.

Q. find the surface charge density on the sheet in C/m^2

What i did was use the formula F = qe with 2.1e-12 for the force and 6.1e-19 for the charge of an electron. This gives me E,which I used in the formula E = (surface charge density)/2epsilon_0.

Plugging everything in (epsilon_0 = 8.85e-12), I get 2.32e-42, but It says it is wrong.

Does anyone know why?

Thanks.
 
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  • #2


Your formulas are correct, so there's a calculation error somewhere.

2.32e-42 C/m^2 is less than 1 electron per square kilometer!
 
  • #3


I keep getting it wrong!

Can anyone verify the above is correct?

Much appreciated.
 
  • #4


frasifrasi said:
Can anyone verify the above is correct?

The above is not correct. It's 2.32 x (A different power of 10 then -42)

Can you show some intermediate results? What did you get for the E-field?
 

FAQ: Damn units and surface charge density.

1. What are "damn units" and why are they important in surface charge density calculations?

"Damn units" is a term used by scientists to refer to units that are difficult to work with or understand. In the context of surface charge density, these units can include coulombs per square meter or volts per meter. It is important to pay attention to the units used in surface charge density calculations because using the wrong units can lead to incorrect results.

2. How is surface charge density defined and measured?

Surface charge density is defined as the amount of electric charge per unit area on a surface. It is usually measured in units of coulombs per square meter. This can be measured experimentally using techniques such as Kelvin probe or surface potential measurements.

3. How does surface charge density affect the behavior of materials?

Surface charge density can greatly influence the properties and behavior of materials. For example, it can affect the adhesion of materials, the way they interact with each other, and their electrical conductivity. It is an important factor to consider in many scientific and technological applications.

4. What is the difference between surface charge density and surface potential?

Surface charge density and surface potential are closely related but distinct concepts. Surface charge density is a measure of the amount of electric charge per unit area on a surface, while surface potential is a measure of the electric potential at a particular point on the surface. Surface potential is affected by both the surface charge density and the distance from the surface, while surface charge density only takes into account the amount of charge on the surface.

5. How can surface charge density be controlled or manipulated?

There are various ways to control or manipulate surface charge density, depending on the material and application. Some common methods include using surface treatments or coatings, applying an external electric field, or adjusting the pH of the surrounding environment. Additionally, certain materials may have intrinsic properties that can be used to manipulate surface charge density, such as the presence of polar or charged functional groups.

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