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The electric force between an electron and a proton separated by a distance of 1 mm is Fₑ= _______ N. (K=1/(4πε₀))

Asked in GSEB Board July 2021 · Coulomb's law and superposition

Answer: (3) -10⁶Ke²

Step-by-step solution

Given: charges +e (proton) and -e (electron); r=1 mm=10⁻³ m; K=1/(4πε₀).

Idea: Coulomb's law with signs, F=(Kq₁q₂)/(r²); a negative result means attraction.

Fₑ=(K(+e)(-e))/((10⁻³)²)=(-Ke²)/(10⁻⁶)

Fₑ=-10⁶Ke² N

The minus sign shows that the force is attractive, as it must be for opposite charges.

Why the other options are wrong

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