Definitions [6]
A capacitor that consists of two large, parallel, conducting plates separated by a small distance is called a parallel plate capacitor.
The ratio of the permittivity of a medium to the permittivity of vacuum.
K = ε / ε₀
OR
Dielectric constant is the factor by which the capacitance of a capacitor increases when a dielectric is completely inserted between its plates.
The product of vacuum permittivity and dielectric constant of the medium.
ε = ε₀K
A dielectric is a non-conducting (insulating) material in which charges are bound to their atoms/molecules and cannot move freely. When placed in an external electric field, the molecules of the dielectric get polarised — they develop induced dipole moments that partially oppose the external field.
The process by which the molecules of a dielectric develop induced dipole moments when placed in an external electric field. The induced dipole moments align opposite to the field, creating an opposing induced field EP.
The maximum electric field a dielectric can withstand before it breaks down (becomes conducting). Measured in V/m. Example: Air ≈ 3 × 10⁶ V/m.
Formulae [2]
For two plates separated by distance d:
\[C=\frac{\varepsilon_0A}{d}\]
With a dielectric medium:
\[C=\frac{K\varepsilon_0A}{d}\]
| Quantity | Without Dielectric | With Dielectric (Full Slab, (K)) |
|---|---|---|
| Electric Field | E0 = \[\frac {σ}{ε_0}\] | E0 = \[\frac {E_0}{K}\] |
| Potential Difference | V0 = E0d | V = \[\frac {V_0}{K}\] |
| Capacitance | C0 = \[\frac {ε_0A}{d}\] | C = KC0 = \[\frac {ε_0KA}{d}\] |
| Permittivity | ε0 | ε = Kε0 |
| Stored Energy (for constant charge) | U0 = \[\frac {Q^2}{2C_0}\] | U = \[\frac {U_0}{K}\](Q constant) |
Important Questions [11]
- Find the Mechanical Force per Unit Area of the Charged Conductor.
- The Energy Density at a Point in a Medium of Dielectric Constant 6 is 26.55 × 106 J/M3. Calculate Electric Field Intensity at that Point
- A Parallel Plate Air Condenser Has a Capacity of 20µF. What Will Be a New Capacity If: 1) The Distance Between the Two Plates is Doubled? 2) A Marble Slab of Dielectric
- Draw a Neat Labelled Diagram of a Parallel Plate Capacitor Completely Filled with Dielectric.
- Define Capacitance of a Capacitor and Its Si Unit.
- Obtain an Expression for Electric Field Intensity at a Point Outside Uniformly Charged Thin Plane Sheet
- A Cube of Marble Having Each Side 1 Cm is Kept in an Electric Field of Intensity 300 V/M. Determine the Energy Contained in the Cube of Dielectric Constant 8.
- What is the Charge on the Capacitor?
- Intensity of Electric Field at a Point Close to and Outside a Charged Conducting Cylinder is Proportional To
- A network of four capacitors of 6 μF each is connected to a 240 V supply. Determine the charge on each capacitor.
- With the Help of a Neat Diagram, Describe the Construction and Working of Van De Graff Generator.
