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All About Capacitors Electrostatics and Electric Lines of Force

Some Important Characteristics of Capacitors
1.The current through capacitor is zero, if the voltage across it is not changing with time.
2. A capacitor is sort of open circuit to direct current.
3. The capacitor never dissipates energy but only stores it.
4. A capacitor resits an abrupt change in voltage across it.
5. A finite amount of energy can be stored in a capacitor even if the current through capacitor is zero, such as when the voltage across it is constant.
6. It is impossible to change the voltage across a capacitor by a finite amount in zero time, for this requires infinite current through the capacitor.

Electrostatics Question and Answer
1. Relative permitivity of vacuum is unity.
2. In the electric field, the potential is the work done in joules to bring positive charge of one coulomb from infinity to that point.
3. The unit of field intensity is newtons/coulomb.
4. Coulomb's law for the force between electric charges most closely resemble with Newton's law of gravitation.
5. Mica medium has highest value of dielectric strength.
6. The maximum value of potential gradient in cable occurs in conductor.
7.A region around a stationary electric charge has electric field.
8. Inside a hollow spherical conductor electric field is zero.
9. The effect of the dielectric is to reduce the working voltage.
10. Electrolytic capacitor is the most commonly used type but it has two disadvantages, namely low insulation resistance and suitable for Direct current only has high capacitance and low insulation resistance.
11. In a radio a gang condenser is a type of air capacitor.
12. A sphere of one metre redius can attain a maximum potential of three kilo volt.
13.The power dissipated in a pure capacitor is zero.
14. In a capacitor the eletric charge is stored in dielectric.
15. One farad is one coulomb per volt.
16. If a dielectri is placed in an electric field, the field strength decreases.
17. If the medium of a parallel plate capacitor consists of mica and air, the capacitance is increased by increasing the area of plates.
18. A capacitor with capacitance is charged through a resistance. The time constant of the charging
circuit is given by RC.

Properties of Electric Lines of Forces
A line of force is supposed to start or emanate, from a unit with a positive charge. A line of force does not form closed loop unlike a magnetic line of force. The line of force is always normal to the surface of the body at the point from where they originate or terminate. No two lines of force can across each other. An electric line of force in the same direction repel each other and those in opposite direction attract each other. There will be neutral point in this case between the two sphere. An electric line of force has a tendecy to take an easy path.

1 comment:

Mark said...

This is a great post! I spent loads of time last year doing electrician training courses and qualifications and this has really shed some light on basic training!

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