5.1 Electric Fields

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A current of 3.0 A flows in a copper wire of cross-sectional area 1.5 × 10⁻⁶ m². Assume that the charge carriers are delocalised electrons with a charge of −1.6 × 10⁻¹⁹ C, moving with an average drift velocity of 1.0 × 10⁻⁴ ms⁻¹.

When working with the very small energies needed to move electrons, the unit electronvolt (eV) is often used rather than the joule (J).

The following descriptions apply to either direct current (dc), alternating current (ac) or both.

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When calculating the electrostatic force between two charged bodies, a constant k called Coulomb's constant is taken into account. 

An electron experiences a force of 0.3 N in an electric field.

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In a vacuum, an alpha particle approaches an aluminium nucleus. 

• The charge on the nucleus
• The charge on the alpha particle
• The nature of the force between them

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• q₁ = 3.2 × 10⁻¹⁹ C
• q₂ = 2.08 × 10^–18 C
• r = 2.0 × 10^–3 m
• k = 8.99 × 10⁹ N m² C^–2

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