Finding Electric Energy Density

In summary: You don't have units on Q. I can't tell you if it's right. It's given as 7.30 nC. How many coulombs is that?
  • #1
stylez03
139
0

Homework Statement


Find the electric-field energy density at a point which is a distance of 10.0 cm from an isolated point charge of magnitude 7.30 nC.


Homework Equations



[tex] u = \frac {1} {2} * e_{o} * E^{2} [/tex]


The Attempt at a Solution



[tex] u = \frac {1} {2} * 8.85*10^{-12} * 7.30^{2} [/tex]

This was the equation we learned in class, and the online program say's its wrong. From the book it says that factors of A and d cancel out because of geometry, though I'm second guessing now, since the book says the equation is only in a vacuum, but this problem doesn't state either or?
 
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  • #2
First you want to know what the value for E is in that situation. What formula might you use for that?
 
  • #3
Dick said:
First you want to know what the value for E is in that situation. What formula might you use for that?

The only equation from this chapter that I could find that would be relevant and give you E would be:

[tex] V_{ab} = E*d [/tex]

[tex] E = \frac {V_{ab}} {d} [/tex] ?
 
  • #4
It's the electric field around a POINT charge. It HAS to be one of the first formulas you encounter. Hint: it's an inverse square law. Keep looking.
 
  • #5
Dick said:
It's the electric field around a POINT charge. It HAS to be one of the first formulas you encounter. Hint: it's an inverse square law. Keep looking.

E = sigma / e_o ?
 
  • #6
stylez03 said:
E = sigma / e_o ?

Nope. E=??/r^2. What's the numerator?
 
  • #7
Dick said:
Nope. E=??/r^2. What's the numerator?

ooh [tex] E = \frac {KQ} {R^{2}} [/tex]

I was thinking about this one but I thought you just meant in this chapter.

Q = 7.30 * 10^-19 ?
 
  • #8
stylez03 said:
ooh [tex] E = \frac {KQ} {R^{2}} [/tex]

I was thinking about this one but I thought you just meant in this chapter.

Q = 7.30 * 10^-19 ?

You don't have units on Q. I can't tell you if it's right. It's given as 7.30 nC. How many coulombs is that?
 

What is electric energy density?

Electric energy density is a measure of the amount of electrical energy that can be stored in a given space or volume. It is typically measured in joules per cubic meter (J/m3).

How is electric energy density calculated?

Electric energy density is calculated by dividing the amount of electrical energy stored in a system by the volume of the system. This can be represented by the formula E/V, where E is the energy and V is the volume.

What factors affect electric energy density?

Electric energy density can be affected by several factors, such as the type of material used for energy storage, the size and shape of the system, and the temperature and pressure of the system.

Why is electric energy density important?

Electric energy density is important because it determines how much energy can be stored in a given space, which is crucial for the design and efficiency of electrical systems and devices.

How can electric energy density be increased?

Electric energy density can be increased by using materials with higher energy storage capabilities, optimizing the size and shape of the system, and controlling the environmental factors such as temperature and pressure.

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