Two identical non-conducting solid spheres of same mass and charge are suspended in air from a common point by two non-conducting, massless strings of same length. At equilibrium, the angle between the strings is α. The spheres are now immersed in a dielectric liquid of density 800 kg m⁻³ and dielectric constant 21. If the angle between the strings remains the same after the immersion, then
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Question

Two identical non-conducting solid spheres of same mass and charge are suspended in air from a common point by two non-conducting, massless strings of same length. At equilibrium, the angle between the strings is α. The spheres are now immersed in a dielectric liquid of density 800 kg m⁻³ and dielectric constant 21. If the angle between the strings remains the same after the immersion, then

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G1 Physics · Accepted Answer

Step 1: Coulomb force in a medium is F = kq₁q₂/(K r²). Step 2: Equating it to the original air/vacuum force kq₁q₂/r₀² gives K r'² = r₀², so r' = r₀/√K. Final: B: electric force between the spheres reduces; C: mass density of the spheres is 840 kg m⁻³.