18.3 A2 Level

Electric force between point charges

7 flashcards to master this topic

Key Concept Flip

For a uniformly charged spherical conductor, where can the entire charge be considered to be located when calculating the electric field or force outside the sphere?

Answer Flip

For points outside the sphere, the entire charge can be considered to be located at the center of the sphere. This simplifies calculations by treating the sphere as a point charge.

Definition Flip

State Coulomb's Law in words.

Answer Flip

Coulomb's Law states that the electric force between two point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them.

Calculation Flip

Write the formula for Coulomb's Law, defining all terms.

Answer Flip

F = Q₁Q₂ / (4πε₀r²), where: F is the electric force, Q₁ and Q₂ are the magnitudes of the charges, r is the distance between the charges, and ε₀ is the permittivity of free space.

Definition Flip

What is the value of the permittivity of free space (ε₀)? Include units.

Answer Flip

The permittivity of free space (ε₀) is approximately 8.85 x 10⁻¹² C² N⁻¹ m⁻².

Calculation Flip

Two point charges, +2 μC and -4 μC, are separated by a distance of 0.5 m in a vacuum. Calculate the magnitude of the electric force between them.

Answer Flip

Using Coulomb's Law: F = (2 x 10⁻⁶ C)(4 x 10⁻⁶ C) / (4π(8.85 x 10⁻¹² C² N⁻¹ m⁻²)(0.5 m)²) ≈ 0.288 N

Key Concept Flip

How does the electric force change if the distance between two point charges is doubled?

Answer Flip

If the distance is doubled, the electric force is reduced by a factor of four (inverse square law). F ∝ 1/r² so if r becomes 2r, F becomes F/4.

Key Concept Flip

Two identical spheres carry equal charge. They are separated by a certain distance. If the charge on each sphere is doubled, how does the electric force between them change?

Answer Flip

The electric force is quadrupled. Since the force is proportional to the product of the charges, doubling both charges results in a force that is 2*2 = 4 times larger.

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18.2 Uniform electric fields 18.4 Electric field of a point charge