Physics Self-Test - Page 14

Explanation: Dielectrics are electrical insulators (non-conducting substances) that do not have free charge carriers for conduction, but can sustain an internal electric field via microscopic polarization.

Explanation: Inside a charged conducting sphere, the internal electric field is zero ($E = 0$). Since $E = -\frac{dV}{dr}$, the potential gradient must be zero, meaning the electric potential remains constant from the center to the surface ($V = \frac{q}{4\pi\varepsilon_0 R}$).

Explanation: Electric field lines always point in the direction of decreasing potential. Therefore, point A is at a higher potential than point B ($V_A > V_B$). The magnitude of the drop over distance $d$ in a uniform field is simply $\Delta V = Ed$, giving $V_A - V_B = Ed$.

Explanation: Since $E = -\frac{\Delta V}{\Delta r}$, if the electric field $E$ between two points is zero, there is no change in potential along that path ($\Delta V = 0$). Hence, the potential at both locations must be identical ($V_A = V_B$).

Explanation: Moving a charge against the opposing electrostatic Coulomb force requires an external force to counteract the field. Therefore, positive work is done *on* the system by an external agent, increasing its electrostatic potential energy.