## Wednesday, 30 March 2016

● Charge : The inherent property of matter due to  which interaction among the particles takes place.
Symbol : Q
S . I . Unit : Coulmb ( c )
Types :
1. Positive Charge
2. Negative Charge
Properties :
1. Like charges repel each other.
2. Unlike Charges attract each other.

Note : 1.6×10^-19 charge is carried by 1 electron.

● Electric Field : The space around a charged body in which a force of interaction can be felt by another charged body is known as electric field.

● Electric Potential : Electric Potential at a point is the work done by bringing a unit positive charge from infinity to that point.

Electric potential = ( work done/Charge )

S . I . Unit = JC^-1 = Volt

◆ 1 Volt at a Point : An electric potential at a point is said to be 1 volt if 1 J of work is done by bringing a unit positive charge from infinity to that point.

● Potential Difference or Voltage : The potential difference between two point is the work done by bringing a unit positive charge from one point to another point.

PD = ( W/Q )
1 volt = JC^-1

Potential difference between two point is said to be 1 volt if 1J of electric work is done to carry unit positive charge from one point to another.

● Electric Current ( I ) :  Charge in motion constitutes an Electric Current.
Def :- The magnitude of charge flowing through a conductor in one second.

I = ( Q/C )
S.I.Unit = ( Coulmb/second ) = ampere ( A )

One ampere : Electric current flowing through a conductor is said  to be 1 ampere if 1 columb of charge flows through it in 1s.

It is potential difference between the ends of a conductor which causes an electric charge to flow..

◆ Other smaller unit of Electric current is milliampere.            1ma = 10^-3 A

● Ammeter : An electric instrument which measures the flow of current through conductor is known as ammeter.

● Voltmeter : An instrument which is used to measure the potential difference between the ends of a conductor.

● Galvanometer: An instrument which detects the flow of current through the conductor.

● Direction of flow of Electric Current :

Conventional direction of flow of electric current is opposite to the direction of flow of electron.
Since an electron flows from cathode to anode so electric current will flow from Anode to Cathode.

● Cell : A device which maintains the potential difference between the ends of conductor.
OR
A device which converts chemical energy to electric energy.

Symbol :       -||-
● Battery: Combination of cells is known as battery.

● Electric Circuit: A closed continuous path consisting of conducting wires electrical appliances such as fans, bulbs etc. along which current flows is known as electric circuit.

● OHM's Law :

At constant temperature, current flowing through a conductor is directly proportional to the potential difference between ends of a conductor.

I = ( 1/R ) V
💭where 1/R is constant.

R is called Resistance of conducting wire
V = IR

● Resistance : The property of a conducting wire due to which it opposes the flow of current through it is known as resistance.

R = ( V/I )
S.I.Unit = Ohm
1 Ohm : resistance of a conducting wire is said to be 1 ohm if a current of 1A flows through it when it is connected to a cell of 1 volt.

● Reasons of resistance:

It produces in the conducting wire due to the collision of the particles.

•• Factors affecting resistance of a wire

> length of a wire.
> area of cross section of wire.
> Nature of conducting wire.
> Temperature.

● Conductor : Those substance which has comparatively low resistance is called conductor.

● Insulator : Those substance which has comparatively more electrical resistance is called insulator.

● Resistivity :
R = pl/A
Where p is constant called resistivity of wire.
S.I. Unit = ohm-meter.

● Combination of resistance:

【1】 Series combination :

Resistors are said to be connected in series if they are connected end to end.

Rule:- same current flows through each resistor.

R = R1 + R2 + R3..........

【2】 Parallel combination :

Resistors are said to be connected in parallel if same potential difference exist between the ends of each resistor and the resistors are connected between two points.

1/R = 1/R1 + 1/R2 + 1/R3..........