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Old Apr 20th 2009, 12:32 PM   #1
Junior Member
Join Date: Apr 2009
Posts: 2
Question Oil drop question,...help!!

Hi i'm a newbie here...Is any one here taking A level Physics (9702)???? If so, please let me know...

Anywayz heres the question:
(a) A charged oil drop of mass 2 x 10^-15 kg is stationary between 2 horizontal metal plates supported parallel to each other in air. The plates are 5mm apart and the top plate is at a potential of +208V relative to the lower plate. Calculate the magnitude of charge on the drop and state the sign of the charge.

**How to know the sign of the charge??Doesn't oil drop have only electrons so its a negative charge!! I'm confused!!....heres the next part: **

(b)both plates described in (a) are tilted so it is 30 deg to the horizontal, parallel to each other and with the same separation.
Calculate (i)direction and magnitude of the initial acceleration of the drop and
(ii) the potential diff. which would have to be applied across the plates so that the drop acquired no vertical component of velocity.

Please explain the solution to this question.....
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Old Apr 20th 2009, 09:48 PM   #2
Senior Member
Join Date: Feb 2009
Location: Singapore
Posts: 206
i just learned this
for the drop to stay stationary, mg=coulomb force.
Q=mgd/V, the sign of the charge is +ve, if i remember correctly

(b)i) direction would be 30degrees to the horizontal, magnitude is calculated by g*sin30.
ii) i don't really know how to do this part, other members please help
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