Question

1.
The value of constant 'K' in coulomb law is
(a) 0.9 x 10° NmC? (b) 9 x 10-9 Nm²C2
(c) 9 x 10° Nm-2 C-2 (d) 9 x 109 Nm² C-2​

Answer 1

Answer :

(d) $\sf{9 \times 10^9 Nm^2 C^{-2}}$

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Derivation of Coulomb's law :

• Force is directly proportional to the magnitude of product of charges.

• Force is inversely proportional to the square distance between charges.

$\implies \sf{F \propto Q_1 Q_2} \\ \\ \\ \implies \sf{F \propto \dfrac{1}{r^2}} \\ \\ \\ \implies \sf{F \propto \dfrac{Q_1 Q_2}{r^2}} \\ \\ \\ \implies \sf{F = \dfrac{1}{4 \pi \epsilon _0} \dfrac{Q_1 Q_2}{r^2}} \\ \\ \\ \implies \sf{F = k \dfrac{Q_1 Q_2}{r^2}}$