What is the charge on a suspended raindrop between two parallel plates?

In summary, two parallel plates with a potential difference of 100 kV and a separation of 0.10 m are given. A suspended raindrop with a diameter of 1.0 mm must carry a charge in order for the resultant force on it to be zero. By balancing the work done by the electric field with the work done by gravity, the charge of the raindrop can be determined. The mass of the raindrop can be found by multiplying its volume by the density of water. The electric field can be calculated using the formula - Δv / Δx.
  • #1
shyguy79
102
0

Homework Statement


Two parallel plates are placed 0.10 m apart with one vertically above the other and their edges aligned. The potential difference of the upper plate is 100 kV relative to the lower plate. What charge must a spherical raindrop of diameter 1.0 mm carry if it remains suspended between the plates? Assume that the electric field between the plates is uniform and give your answer in units of the charge on an electron. (The density of water is 1000 kg m−3

Homework Equations


C = q/V
C = e0 et(A/D)

The Attempt at a Solution


I know that I've got to work out the capacitance in order to work out the charge q=CV but how do I find the capacitance?

I understand Capacitance = permitivity of free space x relative permitivity (Area/Distance of plate separation)

I think I need to find the area and the permitivity but I don't understand why they've given the density of water?

Help please!
 
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  • #2
hi shyguy79! :smile:

i think you're making this too complicated :redface: …

forget about capacitance, it's just a mechanics question …

what is the definition of voltage? :wink:
 
  • #3
shyguy79 said:
[
I know that I've got to work out the capacitance in order to work out the charge q=CV but how do I find the capacitance?


You do not need the charge on the capacitor.
There is a raindrop suspended between the plates. It carries so much charge that the resultant force on it is zero. The charge of the raindrop is the question.

ehild
 
  • #4
Err... The 'work' done to move a charge between to points? Why?
 
  • #5
shyguy79 said:
Err... The 'work' done to move a charge between to points? Why?

ok! :smile:

now balance that against the work done by gravity :wink:
 
  • #6
ehild said:
You do not need the charge on the capacitor.
There is a raindrop suspended between the plates. It carries so much charge that the resultant force on it is zero. The charge of the raindrop is the question.

ehild

So why are we given the density of the water, the separation of the plates, the diameter of the raindrop and the potential between the plates? This is so frustrating!

Thank you all for your help!
 
  • #7
So to balance the raindrop then the charge x electric field = mass x gravity? Or something!
 
  • #8
Yup! :biggrin:
 
  • #9
But the mass of the raindrop? And why the distance between the plates
 
Last edited:
  • #10
volume times density? :wink:
 
  • #11
Ahhhhhhh! Gotcha!
 
  • #12
And so the Electric field = - Δv / Δx ?
 

What is a capacitor?

A capacitor is an electronic component that stores electric charge. It is made up of two conductive plates separated by an insulating material, known as a dielectric. When a voltage is applied to a capacitor, it stores energy in the form of an electric field between the plates.

How does a capacitor store charge?

A capacitor stores charge by creating an electric field between its two plates. When a voltage is applied, one plate becomes positively charged and the other becomes negatively charged. This creates an electric potential difference, or voltage, between the plates, which allows the capacitor to store energy.

What is the unit of measurement for charge in a capacitor?

The unit of measurement for charge in a capacitor is the coulomb (C). One coulomb is equal to the charge of approximately 6.24 x 10^18 electrons.

How does the charge in a capacitor change over time?

The charge in a capacitor changes over time in a predictable manner. When a capacitor is initially charged, the current flowing into it is at its maximum, but as the capacitor becomes fully charged, the current decreases until it reaches zero. When the capacitor is discharged, the current flows out of it in the opposite direction, starting at its maximum and decreasing until it reaches zero again.

What factors affect the charge in a capacitor?

The charge in a capacitor is affected by the capacitance of the capacitor, the voltage applied to it, and the type of dielectric material used. A higher capacitance means the capacitor can store more charge, and a higher voltage results in a higher stored charge. The type of dielectric material also affects the capacitance and therefore the charge that can be stored in a capacitor.

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