Parallel Plate Capacitor

• What is the measure of how easy it is to generate an electric field in a material?

  Permittivity
• What is the relative permittivity sometimes known as?

  Dielectric constant
• How is relative permittivity defined for a given material?

  As the ratio of material permittivity to free space permittivity
• What is the formula for relative permittivity?

  ε = ε / ε₀
• What does the relative permittivity have in terms of units?

  No units, it's a ratio
• What are the steps to find the permittivity of a material from relative permittivity?

  1. Write down the relative permittivity equation
  2. Rearrange for permittivity of the material ε
  3. Substitute in the values

  
• If a material has a relative permittivity of $4.5 \times 10^{11}$, what is its permittivity?


  $3.9825 \times 10^{-11} \text{ F m}^{-1}$
• What happens to polar molecules in a dielectric when an electric field is applied?

  They align with the electric field

  
• What effect does the electric field of polar molecules have on the electric field from capacitor plates?

  It opposes the electric field from the plates

  
• How does the opposing electric field affect the overall electric field in a capacitor?

  It reduces the overall electric field
• What is the result of the opposing electric field on the potential difference between capacitor plates?

  It decreases the potential difference
• How does the capacitance of the plates change due to the dielectric?

  It increases the capacitance
• What is the formula for capacitance in terms of relative permittivity?

  C = $\frac{\varepsilon_r \varepsilon_0 A}{d}$

  • C = capacitance (F)
  • A = cross-sectional area of plates (m²)
  • d = separation of plates (m)
  • ε₀ = permittivity of free space (F/m)
• What does a parallel plate capacitor consist of?

  Conductive plates with a dielectric between them

  
• How is the cross-sectional area of square plates calculated?

  As $L^2$ where L is the length
• How do you determine the relative permittivity of a dielectric in a capacitor?

  1. Compare capacitance of two capacitors
  2. Use the formula for capacitance
  3. Rearrange to find relative permittivity

  
• What should you remember about the cross-sectional area in capacitance equations?

  Use area for one plate only