Electricity
The continuous flow of charge in per unit time is called electricity.
Charge :-
charge is the property of matter which experience both electric and magnetic field.
• Charge is denoted by 'Q'.
• charge is formed by disturbing the neutrality of atom by providing heat.
• the atom which lose its electron positive charge is formed and the atom which gains electron negative charge acquire.
• the atom which lose its electron positive charge is formed and the atom which gains electron negative charge acquire.
e 
• SI unit of current - coulomb/sec = Ampere
• current is denoted by 'I'
More about charge :-
Electric charge -
Electricity is the cause of something present in the matter called electric charge.
• charge is the property of matter due to which it produce and experience both magnetic and electric effect.
• two types of charge
1. Positive charge
2. Negative charge
• Every atom is neutral due to equal number of protons and electrons.
• charge can be produced by disturbing the stability of an atom.
• in case of electron gain positive charge acquire.
Number of electron > number of proton
• In case of electrons lose positive charge acquire.
Number of proton > number of electron
• SI unit of charge = coulomb
• 1 Milli coulomb = 10-³ C
• 1 micro coulomb = 10-⁶ C
Properties of charge :-
- Charge are conserved
- Charge are quantized
- Unlike charge attract each other and like charges repel each other.
- A charge at rest produce an electric field in a space around it.
- Moving charge produce electric field as well as magnetic field around it.
Method of charging :-
1. By friction (opposite charge generate)
2. By conduction (similar charge generate)
3. Buy induction
2. By conduction :-
3. Buy induction :-
Coulomb's law :-
• the force between two charges is directly proportional to the product of charge and inversely proportional to the square of distance between them.
Electric field :-
• the strength of electric current can be expressed by any of the physical quantity.
• buy a strength of electric field has mean the extent of force which its can exist on other charges.
1. Electric field strength ( )
2. Electric potential ( )
Electric field intensity :-
• the electric force experienced by a taste charge divided by the taste charge.
Mathematically ................................
Meaning of taste charge :-
• A particle whose charge is so small that if it can't change the electric field due to other charge appreciably.
• electric field intensity is a vector quantity.
• electric field intensity due to a point charge.
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Consider a point charge 'Q' placed at 'A' then find the electric field at a infinity at 'P'.
Let we take a taste charge ................................ That will experience force 'F' due to point charge 'q'
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• The direction of force is always from 'q', if 'q' is positive and would be towards 'A', if it is negative
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Electric potential energy :-
• Electric force is a conservative force.
• change in the electric potential energy is equal to negative work done by electric force in changing the configuration from initial to final.
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Electric potential :-
• Absolute potential at a point cannot be defined if we take some reference point and assign the potential to be zero at this point then we get absolute potential.
• generally we take reference point to be at infinity.
• the negative work done by electric force in bringing unit positive taste charge from infinity to some desired point called electric potential.
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The flow of charge :-
when we place a conductor in an external electric field then redistribution of charges take place within the conductor to make it a field free region is required the electrostatic equilibrium.
• The redistribution of charges in this case takes place for a very small interval of time and for small time interval the charge are moving within the conductor.
Some question arises :-
? What make the charge to move
? Why the movement of charges stop after sometime
? To achieve a steady flow of charge what we have to do
Solution :-
let we consider a conductor placed in an internal electric field.
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there are free electrons inside the conductor which experience and electric force in a direction opposite to electric field.
• Motion of the charges and solving the problem related to flow of charge becomes much more convenient if we analyse the things in terms of potential difference.
Consider a uniform electric field of intensity 'E' in this electric field reason we consider two point 'A' and 'B' at a separation of 'r' and line AB parallel to the electric field direction.
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for the above expression, electric field direction is from high potential to low potential.
• Positive charge when freed in the reason of electric field moves from high potential to low potential reason.
• Negative charge moves from a low potential to high potential reason.
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Electric current :-
• the net rate of flow of charge through any cross section called electric current.
Consider any cross section through which 'ne' electron and 'np' proton are crossing in time ∆t. then net charge between cross section through this point in time ∆t is given by
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• Current is a scalar quantity.
• SI unit of current is ampere (A).
• 1 ampere = 1 coulomb/1 second.
• it is measured by a device called amateur.
• ammeter is connected in series combination in the circuit.
• an ideal ammeter should have very low resistance or negligible resistance.
Note :-
Current is a scalar quantity but a direction is associated with it which nearly represented the direction of flow of positive charge.
• The direction of electric current is same as that of direction of flow of positive charge and opposite to the direction of flow of negative charge.
Resistance :-
• The resistance is the property of matter due to which it resist the flow of charge or current through it, is called resistance.
• resistance is denoted by (R)
• SI unit of resistance is ohm(Ω)
Numerically, the resistance of an object is equal to the ratio of potential difference applied across it to the current through it.
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• it is only a numerical relation it does not mean that resistance of an object depends on the potential difference applied across it.
• any device which offers some specified resistance to an electric circuit is called resistor.
• resistor is represented as................................
Resistance of a conductor depends on various factor :-
1. Nature of material of conductor.
2. Its dimension (length and area)
More the length greater, will be the resistance.
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More the cross-section area, lower will be the resistance.
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3. Temperature - on increasing the temperature resistance increases
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Resistivity depends upon :-
1. Nature of material.
2. Temperature - temperature is directly proportional to resistivity.
→ Resistivity does not depends upon dimension.
→ Resistivity is a scalar quantity.
→ SI unit of Resistivity is ohm-metre (Ωm)
Important concept :-
Let us consider a parallelepiped whose dimension are a×b×c
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