Physics · Electrostatic Potential And Capacitance · NEET
No, but they are linked. Permittivity e (epsilon) has units (C2 N-1 m-2). Dielectric constant K is a pure number with no unit. They connect through K = e/e0, so e = K x e0. K is also called relative permittivity, because it compares the medium's permittivity to that of vacuum.
When you insert a dielectric, it gets polarised and produces a small field that opposes the applied field. This reduces the net field between the plates, so the voltage V drops for the same charge Q. Since C = Q/V, a smaller V means a larger C. Because C always increases, K = C/C0 is always more than 1. For vacuum K = 1 (the reference), for air K is about 1.0006.
No. K is a ratio of two capacitances (or two permittivities) of the same units, so the units cancel. It is dimensionless. In NEET, if an option gives K a unit, that option is wrong.
Vacuum K = 1 exactly (the reference). Air K is about 1.0006, so we treat it as 1 in most problems. Water is about 80. A metal (conductor) behaves like K = infinity because the field inside becomes zero. Higher K means the material stores more charge for the same voltage.
e (permittivity) tells you how easily a medium allows an electric field and carries units. K (dielectric constant) is just e compared to vacuum: K = e/e0. So K tells you the 'boost factor', while e is the actual material property. For NEET, remember e = K e0.
The capacitance of a parallel plate capacitor with air as medium is 6 microF. With the introduction of a dielectric medium, the capacitance becomes 30 microF. The permittivity of the medium is: (e0 = 8.85 x 10^-12 C2 N-1 m-2)
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the factor by which the capacitance of a capacitor increases when a dielectric fully fills the gap: K = C/C0.
K = C/C0 = e/e0 = E0/E, where E0 is the field without the dielectric and E is the reduced field inside it. All three forms give the same K.
Yes. Dielectric constant and relative permittivity mean the same thing and are both written as K (or er). Both are dimensionless.
No, for real insulating dielectrics K is always greater than 1 because inserting the material always increases the capacitance. Vacuum has the minimum value, K = 1.
Capacitance becomes K times larger: C = K C0. A material with K = 5 makes the capacitor store 5 times more charge for the same voltage.
