# Oil drop experiment electron charge

The problem is based on the experiment conducted by Millikan to find the elementary charge.

In the experiment, charged oil droplets are suspended between two charged plates with a known electric field between them. In this way, the charge of each droplet can be calculated (the mass is known). The distance between the plates is given.

A graph of the voltage needed to bring each charge to equilibrium (to cancel out the gravitational force) as a function of the droplet’s mass is attached.

graph b: y=1.47x

graph c: y=1.96x

graph d: y=2.94x

In the experiment, charged oil droplets are suspended between two charged plates with a known electric field between them. In this way, the charge of each droplet can be calculated (the mass is known). The distance between the plates is given.

A graph of the voltage needed to bring each charge to equilibrium (to cancel out the gravitational force) as a function of the droplet’s mass is attached.

graph b: y=1.47x

graph c: y=1.96x

graph d: y=2.94x

**2. Relevant equations**

When each charge is in equilibrium, the upward electric force equals the gravitational force.

F=mg

Eq=mg

Vq/d=mg

V=m*gd/q

**3. The attempt at a solution**

In this way, I can find the charge on each series of droplets. It is evident from the graph that the charge is a quantum value. I am now asked to find the elementary charge from the data given. How do I do so? I have no idea how many excess electrons are on the droplets (The question states that the elementary charge is the charge of one electron).

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