JEE Main 2026 Physics question
Two metal plates (A, B) are kept horizontally with separation of cm, with plate A on the top. An atomizer jet sprays oil (density 1.5 g/cm³) droplets of radius 1 mm horizontally. All oil droplets carry a charge 5 nC. The potentials and are required on plates A and B respectively in order to ensure the droplets do not descend. The values of and are: (Neglect the air resistance to the droplets and take g = 10 m/s²)
Answer: (A)
Solution
m = (4/3)π(10⁻³)³(1500) = 2π×10⁻⁶ kg, so mg = 2π×10⁻⁵ N. Required field E = mg/q = 2π×10⁻⁵/(5×10⁻⁹) = 4000π N/C, upward (B at higher potential than A,
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