ELECTRICITY
Flow of electric current is called electricity
Electric charge:- It is defined as flow of electron
It is denoted By Q
Its SI unit is Coloumb
Electric Current :- Rate of flow of electric charge is called Electric current
It is denoted By Symbol I
It's SI unit is Ampere
CURRENT=CHARGE/TIME
I=Q/t
Charge posses by electron is Negative charge
Charge posses by proton is positive charge
Properties of charge
Like charge repel each other
Unlike charge attract each other
Charge posses by proton is positive charge
Properties of charge
Like charge repel each other
Unlike charge attract each other
Conductors and Insulators
Conductors are those substance through which electrons are free to move anywhere inside the matter like, aluminium, copper etc. All metals are conductors.
Insulators are those substance thorigh which electrons are not free to move anywhere like, plastic, wood etc.
If positive charge flows, direction of electric current(I) is same as direction of flow of charge.
If negative charge flows, direction of I is opposite to direction of flow of charge.
Electric Potential
Work done per unit charge in bringing a unit positive charge from infinity to that point
Potential Difference
Potential difference between two points is the work done per unit charge in bringing unit postive charge from one point to another
1 volt is the Pd between two points if 1 J of work has to be done in taking 1 Coloumb charge from one point to another.
Electric current flows from high potential to low potential.
Potential difference across the terminals of the cell generated due to chemical reaction within the cell. When cell is connected to a conducting wire, current flows
OHM'S LAW
At constant Temperature and Pressure potential difference across a circuit is directly proportional to Current
I.e:- V∝I
V=IR
here R is constant called Resistance
Resistance :- Resistancw is the property of conductor due to which opposes the flow of electric current through it
Its SI unit is Ohm
Factors on whic Electric currents depend
Lenght :- R∝l (i)
Area off cross section :- R∝1/A (ii)
Nature of conductor
Temperature :- With increase in T R increases
Resistance is directly proportional to resitivity R∝p (rho) (iii)
Combining (i) (ii) and (iii)
R=pl/A
Resistivity :- Resistivity of a conductor is equal to resistance having unit lenght and area
Its Si unit os Ohm metre Electric circuit
Electric circuit is a closed and continuous path for flowing of electric current.
CIRCUIT DIAGRAM
Symbols to draw circuit diagram
Ammemetre :- It is an appartus which is used to measure the value of electric current
It is always connected is series
Resitance of An Ideal Ammemetre is 0
Voltmeter: It is an apparatus which is used to measure the pd between two points in an electric circuit.
It is always connected in parallel
Conductors are those substance through which electrons are free to move anywhere inside the matter like, aluminium, copper etc. All metals are conductors.
Insulators are those substance thorigh which electrons are not free to move anywhere like, plastic, wood etc.
If positive charge flows, direction of electric current(I) is same as direction of flow of charge.
If negative charge flows, direction of I is opposite to direction of flow of charge.
Electric Potential
Work done per unit charge in bringing a unit positive charge from infinity to that point
Potential Difference
Potential difference between two points is the work done per unit charge in bringing unit postive charge from one point to another
1 volt is the Pd between two points if 1 J of work has to be done in taking 1 Coloumb charge from one point to another.
Electric current flows from high potential to low potential.
Potential difference across the terminals of the cell generated due to chemical reaction within the cell. When cell is connected to a conducting wire, current flows
OHM'S LAW
At constant Temperature and Pressure potential difference across a circuit is directly proportional to Current
I.e:- V∝I
V=IR
here R is constant called Resistance
Resistance :- Resistancw is the property of conductor due to which opposes the flow of electric current through it
Its SI unit is Ohm
Factors on whic Electric currents depend
Lenght :- R∝l (i)
Area off cross section :- R∝1/A (ii)
Nature of conductor
Temperature :- With increase in T R increases
Resistance is directly proportional to resitivity R∝p (rho) (iii)
Combining (i) (ii) and (iii)
R=pl/A
Resistivity :- Resistivity of a conductor is equal to resistance having unit lenght and area
Its Si unit os Ohm metre Electric circuit
Electric circuit is a closed and continuous path for flowing of electric current.
CIRCUIT DIAGRAM
Symbols to draw circuit diagram
Ammemetre :- It is an appartus which is used to measure the value of electric current
It is always connected is series
Resitance of An Ideal Ammemetre is 0
Voltmeter: It is an apparatus which is used to measure the pd between two points in an electric circuit.
It is always connected in parallel
Resistance of a System of Resistors
Resistors are joined in two ways that is resitance in series and in parallel.
Resistors in Series: When resistors are joined end to end, they are called resistance in series
Value of current in the ammeter is same So we can say that in a series combination of resistors the current is same in every part of the circuit or same current flow through each resistor. If we add potential difference across each one of resistors (R1, R2 and R3) then we get
V = V1 + V2 + V3
Or i R = i R1 + i R2 + i R3
R = R1 + R2 + R3
So in this case, the total resistance of the system is equal to the sum of the resistance of all the resistors in the system.
If n resistors are connected in series combination then,
R = R1 + R2 + R3 + …………+ Rn
V = V1 + V2 + V3
Or i R = i R1 + i R2 + i R3
R = R1 + R2 + R3
So in this case, the total resistance of the system is equal to the sum of the resistance of all the resistors in the system.
If n resistors are connected in series combination then,
R = R1 + R2 + R3 + …………+ Rn
Resistors in parallel: When resistors are joined in same loop it is called resitance in parralel
In parallel connection, the potential difference across each resistor is equal to the voltage of the battery applied.
When resistors are connected in parallel connection the sum of the currents flowing through all the resistances is equal to total current flowing in the circuit.
i = i1 + i2 + i3
Or V/R = V/R1 + V/R2 + V/R3
=> 1/Rs = 1/R1 + 1/R2 + 1/R3
If n resistors are connected in parallel combination then,
1/Rs = 1/R1 + 1/R2 + 1/R3 + ........... + 1/Rn
Note : When number of resistors are connected in parallel then their combined resistance is less than the smallest individual resistance.i.e Resistance got decreased
Advantages of Parallel connection
- In series connection, either all devices are ON or all are OFF. But in parallel connection, devices could be selectively switched ON or OFF.
- In series connection, if one device fails, all devices will turn OFF. But in parallel connection, if one device fails, rest will work fine.
- In series connection, all devices would get same current. But in parallel connection, different devices need different current for their proper working.
That’s why all devices like fan, TV, refrigerator, bulbs are connected in parallel
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