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Two large circular discs separated by a distance of 0 . 01 m are connected to a battery via a switch as shown in the figure. Charged oil drops of density 900 kg m - 3 are released through a tiny hole at the centre of the top disc. Once some oil drops achieve terminal velocity, the switch is closed to apply a voltage of 200 V across the discs. As a result, an oil drop of radius 8 × 10 - 7 m stops moving vertically and

Correct answer

0

Step-by-step solution

q E = m g q = m g E = 900 × 4 3 π 8 × 10 - 7 3 × 10 200 0 . 01 = 900 × 4 3 π × 512 × 10 - 21 × 10 2 × 10 4 N = 900 × 4 3 π × 512 × 10 - 21 × 10 2 × 10 4 × 1 . 6 × 10 - 19 N ≈ 6

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