Suspending a Charged Droplet: Electric Field E Found by Millikan

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In summary, to find the electric field that will suspend a charged droplet in a gravity field, we can use the equation E = ((ρ g)/q) (4/3) ∏ R3. This was the method used by Millikan to determine that all droplets carried integer multiples of negative charge e= -1.6 x 10-coul.
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Homework Statement



A spherical droplet of radius R and effective mass density ρ. carries a total charge q in a gravity field g. What electric field E iz, will suspend the charged droplet? Millikan found by this method that all droplets carried integer multiples ofnegative charge e= -1.6 x 10-coul.

Homework Equations



F=ma

The Attempt at a Solution



I would like to confirm if my attempt is okay or not. Please can you give explanation based on whatever method it is required to be solved in.

q E = ρ g (4/3) ∏ R3

E = ((ρ g)/q) (4/3) ∏ R3
 
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  • #2
4real4sure said:

Homework Statement



A spherical droplet of radius R and effective mass density ρ. carries a total charge q in a gravity field g. What electric field E iz, will suspend the charged droplet? Millikan found by this method that all droplets carried integer multiples ofnegative charge e= -1.6 x 10-coul.

Homework Equations



F=ma

The Attempt at a Solution



I would like to confirm if my attempt is okay or not. Please can you give explanation based on whatever method it is required to be solved in.

q E = ρ g (4/3) ∏ R3

E = ((ρ g)/q) (4/3) ∏ R3

It makes sense to me. You equated the gravitational force to the electric force (in magnitude). You computed the mass by multiplying the density by the volume. I don't see any problems.
 

1. What is the purpose of suspending a charged droplet?

Suspending a charged droplet is a method used in Millikan's oil drop experiment to determine the charge of an electron. By suspending the droplet in an electric field, the force acting on the droplet can be measured and used to calculate the charge of the droplet.

2. How is the electric field (E) found in Millikan's experiment?

The electric field (E) is found by measuring the force acting on the charged droplet and using the equation F=Eq, where F is the force, E is the electric field, and q is the charge of the droplet.

3. What factors can affect the accuracy of the electric field (E) calculation?

The accuracy of the electric field (E) calculation can be affected by factors such as air currents, temperature changes, and the size and shape of the droplet. These factors can cause fluctuations in the force acting on the droplet, leading to errors in the calculation of the electric field.

4. How does suspending a charged droplet help in determining the charge of an electron?

In Millikan's experiment, the charge of the droplet is known to be a multiple of the charge of an electron. By suspending the droplet in an electric field and measuring the force acting on it, the charge of the droplet can be calculated. This can then be used to determine the charge of an electron by dividing the charge of the droplet by the number of excess charges on the droplet.

5. Are there any limitations to using the method of suspending a charged droplet in determining the charge of an electron?

Yes, there are limitations to this method. The accuracy of the calculation depends on the accuracy of the measurements and the assumptions made about the properties of the droplet. Additionally, this method cannot be used for highly charged droplets, as they may become unstable and split into smaller droplets. Furthermore, this method assumes that the droplet has a uniform charge distribution, which may not always be the case.

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