Capacitance - Answers to Q.

  1. What is a simple parallel plate capacitor, and what does it consist of?

    • A simple parallel plate capacitor consists of two equal parallel metal plates separated by a vacuum or air. It stores electrical charge and energy.

  2. How does a capacitor store energy by transferring charge between plates?

    • A capacitor stores energy by transferring charge from one plate to the other. The plates gain equal but opposite charges, resulting in a net charge of zero.

  3. What is the definition of capacitance, and what is the equation for it?

    • Capacitance (C) is the ability of a capacitor to store charge per unit voltage. It is defined by the equation:

      C = Q / V

      where Q is charge and V is voltage.

  4. What is the formula for the capacitance of a parallel plate capacitor with no dielectric?

    • For a capacitor with air or vacuum between the plates, the capacitance is given by:

      C = ε0 A / d

    where ε0 is the permittivity of free space, A is the plate area, and d is the plate separation.

  5. How does a dielectric affect the capacitance of a vacuum-spaced capacitor?

    • A dielectric material increases capacitance by reducing the electric field strength and allowing more charge to be stored for the same voltage.

  6. What is the electric field within a parallel plate capacitor, and what equation describes it?

    • The electric field (E) in a parallel plate capacitor is uniform and is given by:

      E = V / d

      where V is the potential difference and d is the separation between the plates.

  7. What is the equation for the energy stored in a capacitor?

    • The energy (U) stored in a capacitor is given by:

      U = 1/ 2 QV

      where Q is the charge and V is the voltage across the capacitor.

  8. What are the equations for capacitors in series and in parallel?

    • For capacitors in series: 1Ceq = 1/ C1 + 1/ C2 +…

    • For capacitors in parallel: Ceq = C1 + C2 +…

  9. How does a capacitor charge and discharge through a resistor?

    • When connected to a voltage source, a capacitor charges as current flows until fully charged. When disconnected and connected to a resistor, it discharges as stored charge moves through the resistor.

  10. What are the equations for charging and discharging a capacitor, and what is the time constant (RC)?

  • For charging: Q = Q0(1−e−t/RC)

  • For discharging: Q = Q0 e−t/RC

  • The time constant (RC) determines how quickly the capacitor charges or discharges, where R is resistance and C is capacitance.