4.4 Capacitances Practice Questions Flashcards

Vocabulary flashcards defining fundamental concepts, equations, properties, and safety rules related to capacitances based on A-Level Physics questions.

Capacitance

The ratio of charge stored on a conductor to the potential difference across it, expressed mathematically as $C = \frac{Q}{V}$.

Farad

The SI unit of capacitance, defined as one coulomb per volt ($1\,F = 1\,C\,V^{-1}$).

Capacitor

An electrical component designed to store electric charge and electrical potential energy.

Voltage Rating

The maximum potential difference (such as $20\,V$) that can safely be applied across a capacitor without dielectric breakdown.

Electric Potential

The work done per unit positive charge in bringing a small test charge from infinity to a point in an electric field.

Capacitance of an Isolated Sphere

The capacitance of an isolated spherical conductor of radius $r$, given by $C = 4\pi\varepsilon_0 r$.

Energy Stored in a Capacitor

The electrical energy retained by a charged capacitor, given by the equations $W = \frac{1}{2} Q V$ or $W = \frac{1}{2} C V^2$.

Energy Loss During Charging

The condition where half of the energy supplied by a battery ($W = Q V$) is dissipated as thermal energy in connecting wires or resistors, leaving only $\frac{1}{2} Q V$ stored in the capacitor.

Series Combination of Capacitors

A circuit connection where the inverse of total capacitance equals the sum of the inverses of individual capacitances, given by $\frac{1}{C_T} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3}$.

Parallel Combination of Capacitors

A circuit connection where total capacitance equals the direct sum of individual capacitances, given by $C_T = C_1 + C_2 + C_3$.

Voltage Drop Equation

The drop in potential difference $\Delta V$ across a capacitor supplying current $I$ over a time interval $\Delta t$, given by $\Delta V = \frac{I \Delta t}{C}$.

Leakage Current

A small unwanted current (such as $0.40\,mA$) that continuously flows through a capacitor's dielectric, causing it to discharge slowly over time.

Energy Density of a Capacitor

The stored electrical energy per unit volume of the capacitor, calculated by dividing total stored energy by the physical volume of the component.

Safety Warning on Gadgets

A cautionary sign on electrical appliances warning of potential electric shock hazards caused by high-capacity capacitors retaining high charges even after the power supply is disconnected.