What is r in the formula E = ke q/r2?

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Let’s parse what each option is saying about r in the electrostatic field equation E = k_e q / r^2.
Option a: 'The radial quantity of an electric charge inside an electric field.' This is ambiguous and inaccurately describes r. The formula uses a distance measure, not a property called a radial quantity of the charge itself. It also doesn’t specify a distance to a point in space where the field is evaluated.
Option b: 'The rotational velocity of the moving charge which causes an electric field.' Rotation is related to magnetic effects (via moving charges) but the equation E = k_e q / r^2 describes a static, point-charge field. Velocity of the charge isn’t part of this expression, so this is misleading.
Option c: 'The radius of the charge that contributes to the electric field to be calculated.' The idea of a finite-sized charge with a radius is not what r represents in the point-charge formula. The equation treats the source as a point (or as if all the charge is at a single location), so referring to the charge’s radius is not appropriate here.
Option d: 'The distance from a charge to a point where the electric field is to be calculated.' This matches the conventional interpretation: r is the separation between the source charge and the point in space where you want the field value. The denominator r^2 indicates that the field diminishes with the square of this distance, consistent with inverse-square laws.
In summary, a and c mischaracterize r as a property of the charge rather than a spatial distance, while b introduces dynamics (velocity) not present in the static field formula. The correct interpretation in this context is that r is the straight-line distance from the charge to the point where the field is being computed, which is exactly what option d states.

UCIC 202503 PHYS101 Quiz 9

What is r in the formula E = ke q/r2?

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