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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