(ONLY NEED HELP WITH PART C) In a particular Millikan oil-drop apparatus, the pl

Question

(ONLY NEED HELP WITH PART C) In a particular Millikan oil-drop apparatus, the plates are 2.25 cm apart. The oil used has a density of 0.805 g/cm3 , and the atomizer that sprays the oil drops produces drops of diameter 1.00×103 mm . A)What strength of electric field is needed to hold such a drop stationary against gravity if the drop contains five excess electrons? Answer: 5160 V/m B) What should be the potential difference across the plates to produce this electric field? Answer: V= 116 V.

C) If another drop of the same oil requires a plate potential of 64.5 V to hold it stationary, how many excess electrons did it contain?

Express your answer as an integer.

Explanation / Answer

A) m= p*V ; V-volume : p-density ; m-mass

Assume the drop is spherical; V= 4*pi*r3/3

for the equilibrium,

qE= mg; q= 5*1.6*10-19

E= 5160 V/m

B) E=v/d ; v-potential difference

v= 116.1 V

C) E= V/d= 2866.67

qE= mg ;

q= 1.44 x 10-18

excess electrons= q/(1.6x 10-19) = 9 electrons

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