“This time, like all times, is a very good
one if we but know what to do with it”
– Ralph Waldo Emerson
Today I give you a
free response practice question meant for testing your knowledge, understanding
and capacity for application of basic principles in electrostatics:
Two parallel flat metal
plates P1 and P2 , each of area 0.16 m2, are arranged
horizontally (Fig.) in air with a separation of 1.5×10–2 m. [Separation is shown exaggerated in the figure
for convenience]. A constant potential difference of 60 V is established
between the plates so that the electric field in the region between the plates
is directed vertically downwards as
indicated in the figure. Now, answer the following questions:
(a) If the potential
of plate P1 is +10 V, what is the potential of plate P2?
Justify your answer.
(b) Determine the
magnitude of the electric field between the plates.
(c) Determine the
capacitance of the parallel plate capacitor formed by the plates.
(d) Calculate the
increase in the energy stored in the capacitor (formed by the plates P1
and P2) when additional charges equal to ten electronic charges.are
added to it.
(e) A charged oil
droplet of effective weight 3.2×10–14
newton is found to remain stationary in the space between the plates. Determine
the charge on the oil droplet.
The above question
carries 15 points. You may take up to 17 minutes for answering it. Try to
answer it yourself within the stipulated time. I’ll come back shortly with a
model answer for your benefit.
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