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Electrostatics:

In physics, electrostatics deals with the phenomena and properties of stationary or slow-moving charges. It is known as static electricity.

Applications of Electrostatics:

• A photocopier is mainly based on principles of electrostatics.
• Laser Printers, Ink-jet Printers & electrostatics air filters work on the principles of electrostatics.
• Electric capacitors or condensers work on the principles of electrostatics.
• Van de Graff generator work on the principles of electrostatics (The Van De Graff Generator is basically an electrostatic machine that can generate high voltages)
• Spray painting & powdered coatings are done with the principles of electrostatics.
• Sensitive instruments are protected from external electric fields with the help of            electrostatic shielding.
• Atomic structure can be explained.
• Pollution can be controlled.

Electric charge:

• Electric charge is a physical quantity which causes electric force in matter.
• The electric charges at rest are known as static charges.
• Charge is scalar quantity.
• SI unit of charge is coulomb(C).
• Dimensional formula is [AT].

Ã˜  Polarity of charge: The plus or minus sign given to the charge to differentiate two types of charges is known as polarity of a charge.

Ã˜  Neutral Object: Object having no net charge.

Ã˜  There are two types of charges. +ve and –ve.

§  Similar charges repel each other

§  Opposite charges attract each other

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Basic Properties of Charge:

1.     1. Additive Nature: Total charge on an external body is the algebraic sum of charges in different regions of the body.

2.   2. Conservation of charge: The net electric charge (i.e. algebraic sum of +ve & -ve charge) in an isolated system remains constant. In other words Charge can neither be created nor be destroyed.

Examples: A glass rod rubbed with silk gets positive charge, whereas silk is negative charge.

Uranium Decay:

92U238--------------->90Th234 + 2He4

Number of elementary charge before decay (=92)=Number of elementary charge after decay(=90+2).

3.  3. Quantization of charge: Existence of charges in discrete (distinct). Electric charge is not a continuous quantity, but is an integral multiple of minimum charge (e).

Q=±ne

Q=Total charge, n=1,2,3,4,........

e=elementary charge=1.6×10-19C

Notes:

1 A Coulomb of charge contains around 6 × 1018 electrons. Particles don’t have a high magnitude of charge and we use micro coulombs or milli coulombs in order to express charge of a particle.

1 Î¼C = 10-6 C

1 mC = 10-3 C

The principle of quantization can be used to calculate the total amount of charge present in a body and also to calculate a number of electrons or protons in a body.

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4.  4. Invariance of charge: Magnitude of charge on a body does not vary, whatever may be the speed of the body.

Charge on a body at rest= Charge on a body in motion

CGS unit of charge:

1.      Stat-coulomb or electrostatic unit (e.s.u) of charge.

1 C=3 × 109 stat-coulomb

2.      Ab-coulomb or electromagnetic unit (emu) of charge.

1C=1/10 ab-coulomb

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