Sample Calculation on Milikan's Data Analysis

In summary, the problem involves finding the charge on an oil drop and the number of electrons it is "missing". The given values are Vplates = 2400 V, Dplates = 0.020 m, oil density = 850 kg/m3, and oil drop radius = 0.000051 m. Using the equations for electric field and volume, the electric force and mass of the drop can be calculated. To find the charge, the force of gravity can be equated to the electric force and solved for Q. The distance between the masses is equal to the radius of the drop.
  • #1
realslow
27
0

Homework Statement


Find the charge on the oil drop in Coulombs, and the number of electrons it is "missing".
Vplates= 2400 V
Dplates = 0.020 m
Oil Density = 850 kg/m3
Oil Drop Radius = .000051 m (from Stokes’ Law)



Homework Equations


[tex]E[/tex] = V/d
Volume = 4/3πr3
m= density x volume


The Attempt at a Solution


[tex]\Sigma[/tex] = (2400 V)/(0.020 m) = 1.2 x 105
Volume = 4/3 π(0.000051)3 = 1.7456 x 10-12 m3
m = (850 kg/m3)(1.7456 x 10-12 m3) = 1.4838 x 10-19 kg
And this is where I got to... now I know that Fe = Fg and I was thinking I could find Fg, but am stuck :( I would appreciate it if you could help me out!
 
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  • #2
Sorry about the electric field equations.. they came out weird haha
 
  • #3
How much is the electric force on the charged oil drop in terms of its charge? And how much is the force of gravity if the mass is m?

ehild
 
  • #4
I know that Fe = Q[tex]\Sigma[/tex] so if I find Fg I can solve for Q. However, I am confused as to what values I use for Fg. I know the gravitational constant and the two masses (which are equal?), but am confused about the distance between them. Should I be using the radius of the drop or twice the radius?
 
  • #5
Sorry about that.. Fe = QE
 
  • #6
okay I realized I just need to use Fg = mg :)
 

1. How did Robert Millikan use his oil-drop experiment to determine the charge of an electron?

Robert Millikan used his oil-drop experiment to determine the charge of an electron by measuring the rate of fall of oil drops in an electric field. He found that the drops were always a multiple of a certain value, which he determined to be the charge of an electron.

2. What is the significance of Millikan's experiment in the history of physics?

Millikan's experiment was significant because it provided the first accurate measurement of the charge of an electron, which was a crucial value in understanding the atom and developing the field of quantum mechanics. It also helped to disprove the plum pudding model of the atom and support the idea of discrete energy levels within the atom.

3. How did Millikan's data analysis contribute to the understanding of the nature of matter?

Millikan's data analysis provided evidence for the existence of individual particles with a constant charge, which was a groundbreaking concept at the time. It also helped to support the idea of the atom as a discrete entity rather than a continuous mass, leading to a better understanding of the nature of matter.

4. What were some of the challenges Millikan faced in conducting his experiment?

Some of the challenges Millikan faced in his experiment included maintaining a stable electric field, accurately measuring the rate of fall of the oil drops, and dealing with contamination of the oil drops. He also had to account for factors such as air resistance and the effects of temperature on the oil drops.

5. How has Millikan's experiment influenced modern research in physics?

Millikan's experiment has had a significant impact on modern research in physics by providing a foundation for understanding the behavior of subatomic particles and the nature of the atom. It also laid the groundwork for further experiments in particle physics and helped to pave the way for advancements in technology such as the development of the electron microscope.

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