PHYSICS
NOTES
X
, Electricity
Definition of electricity : Electricity is a form of energy that can produce light , heat and can also be
transmitted through conductors like copper wire.
OR
Electricity is the presence and flow of electric charge ( electrons) in one direction. Its best known
form is the flow of electrons through conductors such as copper wires.
Electric charges : The fundamental property of matter that causes it to experience a force of
attraction or repulsion in presence of other matter.
Properties of electric charges :
( 1 ) Charges are of two types viz., positive and negative charge
( 2 ) Like charges repel each other and opposite charges attract each other.
( 3 ) Charge can neither be created nor be destroyed. The charge from one body can be transferred
to another body.
( 4 ) Total charge on any body is an integral multiple of the charge on an electron or proton
( i.e.1.6 x 10-19C) . This is known as quantization of charge.
q = ne
Where q is charge on a body,
n is an integer and value of it can be 0, ±1 , ±2, ±3, ±4, … … … … ..
e is magnitude of charge on an electron or proton, i.e. 1.6 x 10-19 C.
Unit of electric charge is Coulomb and is denoted by C .
Coulomb’s Law : The force of attraction or repulsion between two point charges is directly
proportional to the product of the magnitudes of the charges on the point charges and is inversely
proportional to the square of the distance between the point charges.
If two point charges of the magnitudes 𝑞1 𝑎𝑛𝑑 𝑞2 are placed at a distance of r, then force between
the charges is
F 𝛼 𝑞1 × q2 …………………… ( i )
1
F𝛼 𝑟2
… …. … … ……………….( 𝑖𝑖)
Writing ( i ) & ( ii ) simultaneously we get
𝑞1 𝑞2
F𝛼 𝑟2
… …. … … ……………….( 𝑖𝑖)
𝑞1 𝑞2
F=k 𝑟2
, Where k is proportionality constant , it’s value is 9 × 109 N𝑚2 /𝑐 2
,Electric field : The field around a charge in which influence of it exists is called electric field.
How is electric field around a charge represented ?
The electric field around a charge is represented by imaginary lines or curves known as electric field
lines or electric lines of force.
Properties of electric field lines or electric lines of force
( i ) Electric lines of force emerge from positive charge and merge into negative charge
( ii ) Thee are imaginary lines or curves
( iii ) These are not closed curves
( iv ) These behave like a stretched string.
( v ) The tangent drawn at any point on a field line shows the direction of electric field at that point
from positive charge to negative charge.
( vi ) Two field lines never intersect each other. If two lines of force intersect each other, then there
will be two direction of the electric field at that point, which is not possible.
Electric field intensity : Electric field intensity or electric field strength at any point in an electric
field is equal to the force experienced by an unit positive charge placed at that point.
, Let a positive point charge +𝑞 is placed at point o . Around this positive point charge +𝑞 there is a
field known as electric field. In the electric field of positive point charge +𝑞 we want to find electric
field intensity at point P. For this we consider another positive charge 𝑞𝑜 of very small magnitude or
value placed at point P with distance a distance r from point O. By using Coulomb’s law we can find
the magnitude of force experienced by positive test charge 𝑞𝑜 .
𝑞 𝑞𝑜
F=k 𝑟2
……………………………… ( i )
Force experienced by unit positive charge is equal to electric field intensity at point P and is given by
𝐹
E = 𝑞 …………………………………..( ii )
𝑜
𝑞𝑞𝑜 1
E =k × …………………….. ( iii )
𝑟2 𝑞𝑜
𝑞
E = k𝑟2 ……………………………… ( iv )
+𝑞 O 𝑞𝑜 P
………………….r...........
Electric field intensity is a vector quantity. SI unit of electric field intensity is Nxm2/C .
What do we mean by electric potential ?
Electric potential at any point in an electric field is equal to the work done in bringing unit positive
charge from infinity to that point.
Let a positive point charge +q is placed at point O . At point P in the electric of positive point charge
+q we want to find electric potential. For this we consider another positive charge of very small
magnitude 𝑞0 and known as positive test charge placed at infinity. From infinity positive test charge
is brought to point P . When positive test charge 𝑞0 moves in the electric field of positive point
charge +q , it will experience a force of repulsion and will have to do work against this force of
repulsion. If work done in bringing positive test charge 𝑞0 from infinity to point p be W , then electric
potential V at point P is given by
NOTES
X
, Electricity
Definition of electricity : Electricity is a form of energy that can produce light , heat and can also be
transmitted through conductors like copper wire.
OR
Electricity is the presence and flow of electric charge ( electrons) in one direction. Its best known
form is the flow of electrons through conductors such as copper wires.
Electric charges : The fundamental property of matter that causes it to experience a force of
attraction or repulsion in presence of other matter.
Properties of electric charges :
( 1 ) Charges are of two types viz., positive and negative charge
( 2 ) Like charges repel each other and opposite charges attract each other.
( 3 ) Charge can neither be created nor be destroyed. The charge from one body can be transferred
to another body.
( 4 ) Total charge on any body is an integral multiple of the charge on an electron or proton
( i.e.1.6 x 10-19C) . This is known as quantization of charge.
q = ne
Where q is charge on a body,
n is an integer and value of it can be 0, ±1 , ±2, ±3, ±4, … … … … ..
e is magnitude of charge on an electron or proton, i.e. 1.6 x 10-19 C.
Unit of electric charge is Coulomb and is denoted by C .
Coulomb’s Law : The force of attraction or repulsion between two point charges is directly
proportional to the product of the magnitudes of the charges on the point charges and is inversely
proportional to the square of the distance between the point charges.
If two point charges of the magnitudes 𝑞1 𝑎𝑛𝑑 𝑞2 are placed at a distance of r, then force between
the charges is
F 𝛼 𝑞1 × q2 …………………… ( i )
1
F𝛼 𝑟2
… …. … … ……………….( 𝑖𝑖)
Writing ( i ) & ( ii ) simultaneously we get
𝑞1 𝑞2
F𝛼 𝑟2
… …. … … ……………….( 𝑖𝑖)
𝑞1 𝑞2
F=k 𝑟2
, Where k is proportionality constant , it’s value is 9 × 109 N𝑚2 /𝑐 2
,Electric field : The field around a charge in which influence of it exists is called electric field.
How is electric field around a charge represented ?
The electric field around a charge is represented by imaginary lines or curves known as electric field
lines or electric lines of force.
Properties of electric field lines or electric lines of force
( i ) Electric lines of force emerge from positive charge and merge into negative charge
( ii ) Thee are imaginary lines or curves
( iii ) These are not closed curves
( iv ) These behave like a stretched string.
( v ) The tangent drawn at any point on a field line shows the direction of electric field at that point
from positive charge to negative charge.
( vi ) Two field lines never intersect each other. If two lines of force intersect each other, then there
will be two direction of the electric field at that point, which is not possible.
Electric field intensity : Electric field intensity or electric field strength at any point in an electric
field is equal to the force experienced by an unit positive charge placed at that point.
, Let a positive point charge +𝑞 is placed at point o . Around this positive point charge +𝑞 there is a
field known as electric field. In the electric field of positive point charge +𝑞 we want to find electric
field intensity at point P. For this we consider another positive charge 𝑞𝑜 of very small magnitude or
value placed at point P with distance a distance r from point O. By using Coulomb’s law we can find
the magnitude of force experienced by positive test charge 𝑞𝑜 .
𝑞 𝑞𝑜
F=k 𝑟2
……………………………… ( i )
Force experienced by unit positive charge is equal to electric field intensity at point P and is given by
𝐹
E = 𝑞 …………………………………..( ii )
𝑜
𝑞𝑞𝑜 1
E =k × …………………….. ( iii )
𝑟2 𝑞𝑜
𝑞
E = k𝑟2 ……………………………… ( iv )
+𝑞 O 𝑞𝑜 P
………………….r...........
Electric field intensity is a vector quantity. SI unit of electric field intensity is Nxm2/C .
What do we mean by electric potential ?
Electric potential at any point in an electric field is equal to the work done in bringing unit positive
charge from infinity to that point.
Let a positive point charge +q is placed at point O . At point P in the electric of positive point charge
+q we want to find electric potential. For this we consider another positive charge of very small
magnitude 𝑞0 and known as positive test charge placed at infinity. From infinity positive test charge
is brought to point P . When positive test charge 𝑞0 moves in the electric field of positive point
charge +q , it will experience a force of repulsion and will have to do work against this force of
repulsion. If work done in bringing positive test charge 𝑞0 from infinity to point p be W , then electric
potential V at point P is given by
