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JEE Main 202118 MarchMorning Shift
Exam
JEE Main
Year
2021
Date
18 March
Shift
Morning Shift
Subject
Physics
Chapter
Dual Nature of Matter

JEE Main 2021 · 18 March · Morning Shift · Physics · Dual Nature of Matter

An oil drop of the radius 2mm with a density 3g cm ^ - 3 is held...

An oil drop of the radius 2mm2mm with a density 3gcm−33g {cm}^{- 3} is held stationary under a constant electric field 3.55×105Vm−13 . 55 \times {10}^{5}V{m}^{- 1} in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess? (considerg=9.81ms−2)\left(\text{consider}g = 9 . 81m{s}^{- 2}\right).

Options

  1. A48.8×101148 . 8 \times {10}^{11}
  2. B1.73×10101 . 73 \times {10}^{10}
  3. C17.3×101017 . 3 \times {10}^{10}
  4. D1.73×10121 . 73 \times {10}^{12}

Correct answer

B. 1.73×10101 . 73 \times {10}^{10}

Step-by-step solution

qE=Mg⇒neE=ρ(43\pir3)×gqE = Mg⇒ neE = ρ\left(\dfrac{4}{3}\pir^{3}\right) \times g
⇒n×1.6×10−19×3.55×105=3×103×43×π×(2×10−3)3×9.81⇒ n \times 1 . 6 \times {10}^{- 19} \times 3 . 55 \times {10}^{5}= 3 \times {10}^{3} \times \dfrac{4}{3} \times \pi \times \left(2 \times {10}^{- 3}\right)3 \times 9 . 81
⇒n=173×10(3−9−5+19)⇒n=1.73×1010⇒ n = 173 \times {10}^{( 3 - 9 - 5 + 19 )}⇒ n = 1 . 73 \times {10}^{10}.
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