What is the Polarity of Charges in a Millikan Type Experiment?

[randomgamernerd]

Homework Statement

: [/B].
in a milikan type experiment there are two oil droplets P and Q between the charged horizontal plates, as shown in the figure. Droplet P is in rest while Q is moving upwards. The polarity of charges on P and Q is:
P. Q
a). +. +
b)neutral. -
c). - -
d). +. -
select the correct option.
Please check the image I've attached

Homework Equations

: [/B]Its a concept based question I guess

The Attempt at a Solution

:[/B]
Q is moving towards +ve plate, it must be negatively charged
P is not accelerating. It must be neutral.
So option B should be the correct option.
But the text says its C

 

[gneill]

What forces are acting on each droplet?

 

[mjc123]

Does B indicate a neutral particle?
Must P be neutral? What forces are acting on it besides electrical?

 

[randomgamernerd]

I'm sorry, I didn't get you guys..I think only electrical forces are acting...
option B implies P is neutral and Q is negatively charged.

 

[gneill]

I'm sorry, I didn't get you guys..I think only electrical forces are acting...
option B implies P is neutral and Q is negatively charged.

Oil drops are not massless...

Have you read an overview of the Millikan Oil Drop Experiment?

 

[randomgamernerd]

Oil drops are not massless...

Have you read an overview of the Millikan Oil Drop Experiment?

I' e not read milikan's experiment.
I am only aware of the concept of electric field and electric field lines(the beginnig of electrostatics)..the question has been asked in the text wihout me tion pf Mi Oil exp.

 

[gneill]

I' e not read milikan's experiment.
I am only aware of the concept of electric field and electric field lines(the beginnig of electrostatics)..the question has been asked in the text wihout me tion pf Mi Oil exp.

A quick google search for "millikan oil drop" would be well worth the effort.

In a nutshell, you can't disregard gravity here.

 

[randomgamernerd]

A quick google search for "millikan oil drop" would be well worth the effort.

In a nutshell, you can't disregard gravity here.

ok i will check it out.
But are you sure this question can't be answered without knowledge of the exp?

 

[gneill]

ok i will check it out.
But are you sure this question can't be answered without knowledge of the exp?

It can be answered so long as you get all the assumptions right for the given problem. You assumed that gravity was not a factor, which turned out to be incorrect given the "Millikan context".