What you are expected to learn

At the end of this module, you should be able to:

• Explain the principles of capacitance.

• Identify the basic units of capacitance.

• Identify different types of capacitors.

• Determine total capacitance in series and parallel circuits.

• Explain RC time constants and how they relate to capacitance.

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some

tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

• Capacitance is the ability to store electrical energy in an electrostatic field.

• A capacitor consists of two conductors separated by an insulator.

• The unit of capacitance is the farad (F).

• Because the farad is large, microfarads ( F) and picofarads (pF) are more often used.

• The letter C represents capacitance.

• Capacitance is affected by:

• 1. Area of the capacitor plates

• 2. Distance between the plates

• 3. Types of dielectric materials

• 4. Temperature

• Capacitor types include: electrolytic, paper, plastic, ceramic, and variable.

• The formula for total capacitance in a series circuit is:

• CT = 1/ C1 + 1/ C2 + 1/ C3 . . . 1/ Cn

• The formula for total capacitance in a parallel circuit is:

• CT = C1 +  C2 +  C3 . . .   Cn

• The formula for the RC circuit time constant is:

• t =  RC

• It takes five time constants to fully charge and discharge a capacitor.

• Mica: Not polarized. Especially useful for high frequencies and voltages

• Electrolytic: Polarized. With very high capacitance values.

• Tantalum: Polarized. It is a type of electrolytic capacitor with greater accuracy and lower capacity / volume relation.

• Plastics: not Polarized. Their values differ depending on the type of plastic used (polyester, polycarbonate, polypropylene, polystyrene...)

• Ceramic: Not Polarized. Useful at a very wide range of frequencies.

• Variables: One of the metal plates is movable, which allows the capacitive value of the capacitor to vary

• Varicap: Being really a diode, this element is often used as a variable capacitor.

Simulation Activities

Capacitor

Dielectric in Capacitor

Important Terms

• Capacitance ( C ) the ability of a dielectric to hold or store an electric charge. The more charge stored for a given voltage, the greater the capacitance.

• Capacitor a component that can store electric charge. A capacitor consists of two metal plates separated by an insulator. Capacitors are named according to the type of dielectric used. Common capacitor types include air, ceramic, plastic film, mica, paper, and aluminum electrolytic.

• Charging increasing the amount of charge stored in a capacitor. The accumulation of stored charge results in a buildup of voltage across the capacitor.

• Condenser another (older) name for a capacitor.

• Dielectric absorption the inability of a capacitor to discharge completely to zero. Dielectric absorption is sometimes called battery action or capacitor memory.

• Dielectric material another name for an insulator.

• Discharging the action of neutralizing the charge stored in a capacitor by connecting a conducting path across the capacitor leads.

• Electric field the invisible lines of force between opposite electric charges.

• Farad (F) unit the basic unit of capacitance. 

• Ganged capacitors two or three capacitor sections on one common shaft that can be rotated.

• Leakage current the current that flows through the dielectric of a capacitor when voltage is applied across the capacitor plates.

• Leakage resistance a resistance in parallel with a capacitor that represents all leakage paths through which a capacitor can discharge.

• Microfarad a small unit of capacitance equal to 1 x 10^-6 F.

• Nanofarad (nF) a small unit of capacitance equal to 1 x 10^- 9 F.

• Picofarad (pF) a small unit of capacitance equal to 1 x 10^-12 F.

Self Check