Problem — True or false on charge and field

Problem

True or false? (a) Charges of the same sign repel each other. (b) A neutral body feels no electric forces. (c) The SI unit of charge is the coulomb. (d) The Coulomb force decreases as the inverse square of the distance. (e) The electric field has units of volts.

Solution

(a) True. Charges of the same sign repel, opposite signs attract.

(b) False. A neutral body can still feel electric forces: through induction (conductor) or polarisation (dielectric) the charges inside it separate and a net attraction appears.

(c) True. The SI unit of charge is the coulomb ($\text{C}$).

(d) True. Coulomb’s law gives $F = k\,|q_1 q_2|/r^2$: the force goes as $1/r^2$.

(e) False. The electric field is measured in $\text{N/C}$, equivalent to $\text{V/m}$, not in volts. The volt is the unit of potential.

$\ev{V,\ F,\ V,\ V,\ F}$

Links

Topics: Electric field and potential Concepts: Electric field · Electric charge