**Specifications of Capacitors:**

The specifications of capacitors are:

**1. Capacitor Value:**

It provides the value of a capacitor C as farads moreover printed or colour coded over the body of the capacitor. It's units are Farads. Practical capacitors are available from 1pf to 1000 mF.

**2. Tolerance:**

The variation in capacitance value from the indicated value.

**3. Dielectric Constant:**

It is defined as the ratio of capacitance of a capacitor containing the dielectric material, to the capacitance of the same capacitor with air or vaccum as the dielectric. It is denoted by the letter K. It may be expressed as

K = Capacitance of the capacitor with dielectric/ Capacitance of the capacitor with air dielectric.

The dielectric constant is also known as relative permittivity Ɛ

_{r}.The relative permittivities of some dielectric media are listed in the Table.

Material | Dielectric constant or relative permittivity (Ɛ_{r}) |

Air or vacuum | 1 |

Bakelite | 4.5 – 5.5 |

Ceramic | 50 - 300 |

Fibre | 5 – 8 |

Glass | 7 – 8 |

Mica | 3 – 6 |

Paper (dry) | 2 – 2.5 |

Paper (waxed) | 3 – 5 |

Polystyrene | 2.6 |

Porcelain | 5 – 6 |

Rubber | 2 – 3.5 |

**4. Dielectric Strength:**

It is very important specification of a capacitor (insulator or dielectric medium), which gives the maximum voltage gradient that a unit thickness of the medium can withstand without breaking down. It’s unit is Volt/metre (V/m) although it is usually expressed in KV/m.m.

**Factors affecting the Dielectric Strength:**

a. It decreases with increase in the thickness of dielectric material.

b. It decreases with increase in frequency.

c. It decreases with humidity and temperature

d. It decreases with increasing time of application of electric current.

**5. Power Factor:**

It gives the fraction of input power dissipated as heat loss in the capacitor. The quality of a capacitor in terms of minimum loss is often indicated by its power factor. The lower the numerical value of the power factor the better is the quality of the capacitor.

There are some other specifications that are to be considered while selecting a capacitor. They are.

**6. Temperature Coefficient:**Variation of capacitance value with the temperature.

**7. Voltage Rating:**Maximum voltage that can be applied across a capacitor.

**8. Leakage Resistance/Leakage Current:**Reciprocal terms that denote leakage property of capacitor.

**Uses of Capacitors:**

No | Type | Max Working Voltage in Volts | Typical Uses/ Applications |

1 | Tubular Rolled paper | 1000 | Coupling and decoupling AF circuit |

2 | Metallised paper | 400 | Coupling and decoupling AF circuit |

3 | Polystyrene | 125 – 500 | Resonant circuits, coupling measuring circuit |

4 | Polyester | 500 | Coupling Decoupling and Smoothing |

5 | Stacked Mica | 2000 | RF Coupling Bypassing circuit |

6 | Silvered Mica | 1000 | RF Resonant circuits and Measuring circuits. |

7 | Silvered Ceramic | 1000 | RF amplifiers, RF Bypass Circuits |

8 | Ceramic with high dielectric constant | 350 | |

9 | Aluminium Electrolytic | 600 | Rectifier filters and smoothing |

10 | Tantalum Electrolytic | 6 – 150 | Coupling, decoupling Bypassing in transistor amplifiers and PCB’s |

11 | Air/ Polystyrene variable capacitance | 1000 | Tuning circuits in receivers and transmitters |

12 | Mica Trimmers and padders | 500 | Tracking and alignment of receivers |

13 | Air Trimmers | 500 | Tracking and alignment of receivers |

Tags:
Basic Electronics