2 Electric Potential and Capacitance Free Online FlashCards

What is electric potential?

Electric potential is potential energy per unit charge: $V=\frac{U}{q}$. A potential difference changes a charge’s potential energy by $\Delta U=q\Delta V$.

What is the potential of a point charge?

For a point charge $Q$, the potential at distance $r$ is $V=\frac{1}{4\pi\varepsilon_0}\frac{Q}{r}$, with zero potential chosen at infinity.

How do potentials from multiple point charges combine?

Electric potential is a scalar, so the total potential from several point charges is the algebraic sum of their individual potentials: $V=\frac{1}{4\pi\varepsilon_0}\sum_i\frac{Q_i}{r_i}$.

What is the potential difference along a uniform electric field?

For a uniform field directed from $A$ to $B$ over distance $d$, $V_B-V_A=-Ed$.

Which way does the electric field point relative to potential?

The electric field points toward decreasing electric potential.

What are key properties of a conductor in electrostatic equilibrium?

In electrostatic equilibrium, the electric field inside conducting material is zero, the conductor is an equipotential, and excess charge resides on its surface.

When is an empty cavity in a conductor field-free?

An empty cavity inside a conductor has no electric field when the conductor is in electrostatic equilibrium and no charge is placed inside the cavity.

How is the electric field oriented just outside a conductor?

Just outside a conductor’s surface, the electric field is perpendicular to the surface; a tangential component would move surface charges.

What does capacitance measure, and what determines it?

Capacitance is charge stored per potential difference: $C=\frac{Q}{\Delta V}$. It depends on conductor geometry and the material between them, not on the particular values of $Q$ and $\Delta V$.

How do plate area and separation affect parallel-plate capacitance?

For parallel plates with small edge effects, $C=\varepsilon_0\frac{A}{d}$. Increasing plate area increases capacitance; increasing separation decreases it.

What are equivalent formulas for a capacitor’s stored energy?

A capacitor stores electric potential energy: $U_C=\frac{1}{2}Q\Delta V=\frac{Q^2}{2C}=\frac{1}{2}C(\Delta V)^2$. Choose the form matching the known quantities.

How does a dielectric respond to an electric field?

A dielectric polarizes in the field: bound charges shift slightly and create a field that opposes the original field within the material.