Potential difference and kinetic energy between plates

In summary: Then you'll get the correct answer which is 3.3 kV.In summary, the potential difference between the plates is 3.30 kV and the kinetic energy of the point charge just before it hits the positive plate, assuming no other forces act on it, is determined by the equations given and the charge density on the plates.
  • #1
kbyws37
67
0
A point charge q = −2.40 nC is initially at rest adjacent to the negative plate of a capacitor. The charge per unit area on the plates is 4.50 µC/m2 and the space between the plates is 6.50 mm.
(a) What is the potential difference between the plates?
kV
(b) What is the kinetic energy of the point charge just before it hits the positive plate, assuming no other forces act on it?
µJ


My attempt:

(a)
http://maxwell.byu.edu/~spencerr/websumm122/img204.gif

sigma = Q/A
sigma = -2.4 / 4.5 = -0.533

E = (-0.533) / (8.85 x 10^-12)
E = -6.023x10^10

potential difference = Ed
potential difference = (-6.023x10^10 )(6.50)
potential difference = -3.9 x 10^11

I'm getting it wrong (the correct answer is 3.30 kV)
 
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  • #2
anyone?
please help.
 
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  • #3
??


anyone?
please help.
 
  • #4
kbyws37 said:
A point charge q = −2.40 nC is initially at rest adjacent to the negative plate of a capacitor. The charge per unit area on the plates is 4.50 µC/m2 and the space between the plates is 6.50 mm.
(a) What is the potential difference between the plates?
kV
(b) What is the kinetic energy of the point charge just before it hits the positive plate, assuming no other forces act on it?
µJ


My attempt:

(a)
http://maxwell.byu.edu/~spencerr/websumm122/img204.gif

sigma = Q/A
sigma = -2.4 / 4.5 = -0.533

E = (-0.533) / (8.85 x 10^-12)
E = -6.023x10^10

potential difference = Ed
potential difference = (-6.023x10^10 )(6.50)
potential difference = -3.9 x 10^11

I'm getting it wrong (the correct answer is 3.30 kV)

You have this wrong. The charged particle has nothing to do with the potential difference across the plates. What you want to use is
[tex]E = \frac{\sigma}{\epsilon_o}[/tex]
where [tex]\sigma[/tex] is the charge density on the plates, which was given in the question. So you can find the electric field from that equation, and then use V=Ed to find the potential difference.

NOTE: make sure your units are consistent! You must convert your quantities into SI units (m, kg, s, etc).
 
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  • #5
All the equations are correct but the substitution of the values. You should use sigma=4.5 uC/m2 because it is the charge density (look at its unit).
 

1. What is potential difference between plates?

Potential difference, also known as voltage, is the difference in electric potential energy per unit charge between two points in an electric field. In the case of plates, it refers to the difference in electric potential energy between two parallel plates that have a potential difference applied across them.

2. How is potential difference measured?

Potential difference is measured in units of volts (V) using a voltmeter. A voltmeter is connected across the two plates and measures the difference in electric potential energy between them.

3. What is the relationship between potential difference and kinetic energy between plates?

As potential difference increases between the plates, the kinetic energy of the charged particles between the plates also increases. This is because the potential difference provides the force necessary to accelerate the particles, increasing their kinetic energy.

4. How does the distance between plates affect potential difference and kinetic energy?

The potential difference between plates is directly proportional to the distance between them. This means that as the distance between plates increases, the potential difference and kinetic energy between them also increase. This is because the electric field between the plates is weaker, so more potential difference is needed to accelerate the particles.

5. Can potential difference and kinetic energy between plates be manipulated?

Yes, potential difference and kinetic energy between plates can be manipulated by changing the applied potential difference, the distance between plates, or the type and charge of particles between the plates. This is the basis for many experiments and technologies, such as capacitors and particle accelerators.

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