According to Coulomb's Law, what happens to the electric force if a dielectric medium (like glass or water) is introduced between two point charges? MCQ with Answer and Explanation
According to Coulomb's Law, what happens to the electric force if a dielectric medium (like glass or water) is introduced between two point charges?
A. The force increases.
B. The force decreases.
C. The force remains identical.
D. The force drops immediately to zero.
Answer: Option B
Solution (By JKSSB Mock Tests)
Coulomb's force in a vacuum is F = (1/4piepsilon_0) * (q1q2/r^2). When a dielectric medium with relative permittivity (dielectric constant) 'K' is introduced, the new force is F' = F / K. Since K > 1 for all insulating materials (e.g., K for water is ~80), the electrostatic force between the charges is significantly reduced by the medium.
Assertion (A): The coefficient of kinetic friction is always strictly less than the coefficient of limiting static friction. Reason (R): Once motion starts, the inertia of rest is broken and interlocking of surface irregularities is less effective.
A.A is false but R is true.
B.A is true but R is false.
C.Both A and R are true and R is the correct explanation of A.
D.Both A and R are true but R is NOT the correct explanation of A.
Explanation:
Static friction opposes impending motion, reaching a maximum called limiting friction. Once the object moves, it doesn't have enough time for the microscopic irregularities (asperities) of the two surfaces to interlock strongly. Thus, the force required to keep it moving (kinetic friction) is slightly less than the force required to start the motion.
Explanation:
Myopia (near-sightedness) occurs when the image is focused in front of the retina. It is corrected using a concave (diverging) lens. Hypermetropia (far-sightedness) is corrected with a convex (converging) lens. Astigmatism is corrected with a cylindrical lens. Presbyopia is usually corrected with bifocal lenses.
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