6.1 CAPACITORS

    Cards (51)

    • What is a capacitor?
      An electrical component that stores charge
    • What is the purpose of the dielectric in a capacitor?
      To prevent charge from traveling across the gap
    • How is capacitance defined mathematically?
      Capacitance, CC, is C=C =QV \frac{Q}{V}
    • In what unit is capacitance measured?
      Farads, F
    • What happens when a capacitor is connected to a DC power supply?
      Current flows until potential difference equals e.m.f.
    • What charges do the plates of a capacitor hold after connection to a power supply?
      One plate holds charge +QQ, the other -QQ
    • What is the role of the dielectric in increasing capacitance?
      It polarizes in the electric field
    • What is electrical permittivity?
      It describes a dielectric's ability to polarize
    • Why are materials like air or vacuum poor dielectrics?
      They do not polarize well
    • What does Kirchhoff’s voltage law state?
      The sum of e.m.f.s equals the sum of potential differences
    • How is the total capacitance of capacitors in series calculated?
      Using 1CT=\frac{1}{C_T} =1C1+ \frac{1}{C_1} +1C2+ \frac{1}{C_2} + \ldots
    • What is the formula for combined capacitance in series?
      CT=C_T = \left( \frac{1}{C_1} +1C2+ \frac{1}{C_2} + \ldots \right)^{-1}
    • How is the total capacitance of capacitors in parallel calculated?
      latex>C_T = C_1 + C_2 + C_3 + \ldots</latex>
    • What must be done to charge a capacitor?
      Work must be done by the power supply
    • What does the area under the charge-voltage graph represent?
      Work done in charging the capacitor
    • What is the formula for energy stored in a capacitor?
      W=W =12QV \frac{1}{2} Q V
    • How can the energy stored in a capacitor also be expressed?
      W=W =12V2C \frac{1}{2} V^2 C
    • What is the role of capacitors in camera flashes?
      To store and discharge large energy quickly
    • How do capacitors function in uninterrupted power supplies (UPS)?
      They provide backup power when mains fail
    • What happens to AC current after passing through a full wave rectifier?
      It flows in one direction but varies
    • How do capacitors help maintain a constant current?
      They store energy as p.d. rises and discharge as it falls
    • What occurs when a capacitor is discharged?
      Electrons flow and dissipate energy as heat
    • What determines the time constant of a discharging capacitor?
      Capacitance and resistance in the circuit
    • How does resistance affect the current during discharging?
      Lower resistance allows higher current flow
    • What is the relationship between capacitance and charge stored?
      Higher capacitance means larger charge stored
    • What does the symbol \sim indicate in the context of capacitance?

      It means 'goes as' or proportional
    • Why is the relationship between current and charge not simple during discharging?
      Current is not constant while discharging
    • What is the relationship between resistance and current in a discharging circuit?
      The lower the resistance, the higher the current
    • How does current relate to charge on the plates in a capacitor?
      Higher current leads to faster charge drop
    • What does capacitance measure in a capacitor?
      Charge stored per unit potential difference
    • What is the formula for capacitance?
      C=C =QV \frac{Q}{V}
    • What happens to the charge on a capacitor as it discharges?
      The charge decreases as time progresses
    • What is the maximum potential difference across the plates before discharging?
      V0=V_0 =Q0C \frac{Q_0}{C}
    • What happens to the current as the charge stored on the capacitor decreases?
      The current also decreases over time
    • What is the relationship between current and charge in a discharging capacitor?
      I=I =dQdt -\frac{dQ}{dt}
    • Why is there a negative sign in the current equation for discharging capacitors?
      Conventional current flows opposite to electron flow
    • What is the result of separating variables in the current equation?
      It allows integration to find charge over time
    • What is the final equation for charge in a discharging capacitor?
      Q=Q =Q0etCR Q_0 e^{-\frac{t}{CR}}
    • How are voltage and current related to charge in a capacitor?
      Voltage and current are related by V=V =IR IR
    • What is the equation for voltage in a discharging capacitor?
      V=V =V0etCR V_0 e^{-\frac{t}{CR}}
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