1
ELECTRIC CHARGES AND FIELDS
1 INTRODUCTION
➢ Atoms are building blocks of matter
➢ Atoms are made up of three elementary particles namely 1. Electrons 2.
Protons 3. Neutrons
➢ Mass, Electric Charge, and Spin are intrinsic Properties of elementary
Particles.
➢ Mass is an intrinsic Property which is a measure of quantity of matter present
in a substance.
➢ Like mass, Electric charge is intrinsic Property of elementary particles due to
which they exert electrostatic force on each other through electric field.
➢ Electrons possess negative charge.
➢ Protons Possess positive charge.
➢ Neutrons have no or zero charge.
➢ Atoms in their element state are neutral i,e their net electric charge is zero
because they have equal number of protons and electrons.
➢ When an atom loses electrons, it becomes positively charged due to excess
number of protons and it is called CATION or POSITIVE ION.
➢ When an atom gains electrons, it becomes negatively charged due to excess
number of electrons and it is called ANION or NEGATIVE ION
➢ S I Unit of electric charge is Coulomb (C)
Elementary particle Mass (kg) Electric charge (C)
Electron (e) 9.1 x 10 – 31 kg -1.6 x 10 – 19 C
Proton (p) 1.673 x 10 – 27 Kg + 1.6 x 10 – 19 C
Neutron (n) 1.675 x 10 – 27 Kg zero
➢ Net electric charge of charged object is integral multiple of basic quantity of
electric charge (e)
➢ Net charge of charged object is q = ± ne
where e = 1.6 x 10 – 19 C
and n = 1, 2, 3, .........
, 2
2 Properties of Electric Charge
1. Electric Charge is a scalar quantity
2. Quantization of charge: Net charge of charged object is q = ± ne
where e = 1.6 x 10 – 19 C and n = 1, 2, 3, ..............
3. Conservation of charge: total electric charge during any Physical or
Chemical Process remains same. Charge can neither be created nor
destroyed but only exists in positive and negative pairs.
4. Additive Property of electric charge. The net charge Q of a system of
different number ±q1, ±q2, ±q3, ±q4, ±q5 .......of charges is the algebraic sum
of individual charges.
Q = (±q1) +( ±q2) + (±q3) + (±q4) + (±q5) ......
5. Electric charge resides only on the outer surface of a hallow charged object.
6. Electric charge is uniformly distributed on the surface of an object of
uniform surface area
7. Electric charge density is more at the pointed sharp ends of an object of
non-uniform surface area.
8. Similar electric charges repel each other and opposite electric charges
attract each other with a force called electrostatic force
3 Methods of charging an object
1. Charging by frictional method
2. Charging by induction method
3. Charging by conduction method
, 3
3.1 Charging an object by frictional method
In charging an object when any two suitable objects when rubbed against each
other they get electrically charged due to transfer of electrons from one object
to the other.
When any two objects in the list of materials given below are rubbed against
each other the object occurring earlier in the list get positively charged while
the object occurring later in the list get negative charge.
1. Fur, 2. Flannel, 3. Sealing wax, 4. Glass, 5. Cotton, 6. Paper, 7. Silk 8.
Human body, 9. Wood, 10. Metals, 11. Rubber, 12. Resin, 13. Amber,
14. Sulphur, 15. Ebonite, 16. Guta parcha.
Example: 1. When a glass rod is rubbed with fur then glass rod gets
negatively charged and fur get positively charged
2. When a glass rod is rubbed with silk then glass rod gets positively
charged and fur get negatively charged
3.2 Charging on object by induction method
1. When a charged object is brought closer to an uncharged object
opposite charge is produced at the near end and like charge is produced
at far end.
2. Magnitude of induced charge is less than inducing charge.
3. Large number of charges can be charged at the same time by induction
method of charging.
, 4
3.3 Charging by Conduction method.
When electrically charged, object is connected to an uncharged object electric
charge flows until the two objects get equally charged.
Question: How to detect the presence of charge and nature of charge?
Gold leaf electroscope is used to 1) detect the presence of electric charge 2)
nature of electric charge
4 COULOUMB’S LAW OF ELECTROSTATIC FORCE
➢ It states that the electrostatic force of attraction or repulsion between any two
electric charges is directly proportional to the product of magnitude of electric
charges and inversely proportional to the square of the distance between
charges and permittivity of medium between charges.
𝟏 𝒒𝟏 𝒒𝟐
𝑭=
𝟒𝝅𝜺𝟎 𝒓𝟐
F=Electrostatic force of attraction or repulsion
𝜖0 = 8.854 𝑋10− 12 𝐶 2 𝑚− 2 𝑁 − 1 ; Permittivity of free space
q1 and q2 are magnitude of electric charges
r=distance between the electric charge
1
= 9 𝑋 109 𝑁𝑚2 𝐶 − 2
4𝜋𝜀0
𝟏 𝒒𝟏 𝒒𝟐 𝟏 𝟏 𝒒𝟏 𝒒𝟐
𝑭𝒎𝒆𝒅𝒊𝒖𝒎 = = ( )
𝟒𝝅 𝜺𝒓 𝜺𝟎 𝒓𝟐 𝜺𝒓 𝟒𝝅 𝜺𝟎 𝒓𝟐
𝑭𝒂𝒊𝒓
𝑭𝒎𝒆𝒅𝒊𝒖𝒎 =
𝜺𝒓
ELECTRIC CHARGES AND FIELDS
1 INTRODUCTION
➢ Atoms are building blocks of matter
➢ Atoms are made up of three elementary particles namely 1. Electrons 2.
Protons 3. Neutrons
➢ Mass, Electric Charge, and Spin are intrinsic Properties of elementary
Particles.
➢ Mass is an intrinsic Property which is a measure of quantity of matter present
in a substance.
➢ Like mass, Electric charge is intrinsic Property of elementary particles due to
which they exert electrostatic force on each other through electric field.
➢ Electrons possess negative charge.
➢ Protons Possess positive charge.
➢ Neutrons have no or zero charge.
➢ Atoms in their element state are neutral i,e their net electric charge is zero
because they have equal number of protons and electrons.
➢ When an atom loses electrons, it becomes positively charged due to excess
number of protons and it is called CATION or POSITIVE ION.
➢ When an atom gains electrons, it becomes negatively charged due to excess
number of electrons and it is called ANION or NEGATIVE ION
➢ S I Unit of electric charge is Coulomb (C)
Elementary particle Mass (kg) Electric charge (C)
Electron (e) 9.1 x 10 – 31 kg -1.6 x 10 – 19 C
Proton (p) 1.673 x 10 – 27 Kg + 1.6 x 10 – 19 C
Neutron (n) 1.675 x 10 – 27 Kg zero
➢ Net electric charge of charged object is integral multiple of basic quantity of
electric charge (e)
➢ Net charge of charged object is q = ± ne
where e = 1.6 x 10 – 19 C
and n = 1, 2, 3, .........
, 2
2 Properties of Electric Charge
1. Electric Charge is a scalar quantity
2. Quantization of charge: Net charge of charged object is q = ± ne
where e = 1.6 x 10 – 19 C and n = 1, 2, 3, ..............
3. Conservation of charge: total electric charge during any Physical or
Chemical Process remains same. Charge can neither be created nor
destroyed but only exists in positive and negative pairs.
4. Additive Property of electric charge. The net charge Q of a system of
different number ±q1, ±q2, ±q3, ±q4, ±q5 .......of charges is the algebraic sum
of individual charges.
Q = (±q1) +( ±q2) + (±q3) + (±q4) + (±q5) ......
5. Electric charge resides only on the outer surface of a hallow charged object.
6. Electric charge is uniformly distributed on the surface of an object of
uniform surface area
7. Electric charge density is more at the pointed sharp ends of an object of
non-uniform surface area.
8. Similar electric charges repel each other and opposite electric charges
attract each other with a force called electrostatic force
3 Methods of charging an object
1. Charging by frictional method
2. Charging by induction method
3. Charging by conduction method
, 3
3.1 Charging an object by frictional method
In charging an object when any two suitable objects when rubbed against each
other they get electrically charged due to transfer of electrons from one object
to the other.
When any two objects in the list of materials given below are rubbed against
each other the object occurring earlier in the list get positively charged while
the object occurring later in the list get negative charge.
1. Fur, 2. Flannel, 3. Sealing wax, 4. Glass, 5. Cotton, 6. Paper, 7. Silk 8.
Human body, 9. Wood, 10. Metals, 11. Rubber, 12. Resin, 13. Amber,
14. Sulphur, 15. Ebonite, 16. Guta parcha.
Example: 1. When a glass rod is rubbed with fur then glass rod gets
negatively charged and fur get positively charged
2. When a glass rod is rubbed with silk then glass rod gets positively
charged and fur get negatively charged
3.2 Charging on object by induction method
1. When a charged object is brought closer to an uncharged object
opposite charge is produced at the near end and like charge is produced
at far end.
2. Magnitude of induced charge is less than inducing charge.
3. Large number of charges can be charged at the same time by induction
method of charging.
, 4
3.3 Charging by Conduction method.
When electrically charged, object is connected to an uncharged object electric
charge flows until the two objects get equally charged.
Question: How to detect the presence of charge and nature of charge?
Gold leaf electroscope is used to 1) detect the presence of electric charge 2)
nature of electric charge
4 COULOUMB’S LAW OF ELECTROSTATIC FORCE
➢ It states that the electrostatic force of attraction or repulsion between any two
electric charges is directly proportional to the product of magnitude of electric
charges and inversely proportional to the square of the distance between
charges and permittivity of medium between charges.
𝟏 𝒒𝟏 𝒒𝟐
𝑭=
𝟒𝝅𝜺𝟎 𝒓𝟐
F=Electrostatic force of attraction or repulsion
𝜖0 = 8.854 𝑋10− 12 𝐶 2 𝑚− 2 𝑁 − 1 ; Permittivity of free space
q1 and q2 are magnitude of electric charges
r=distance between the electric charge
1
= 9 𝑋 109 𝑁𝑚2 𝐶 − 2
4𝜋𝜀0
𝟏 𝒒𝟏 𝒒𝟐 𝟏 𝟏 𝒒𝟏 𝒒𝟐
𝑭𝒎𝒆𝒅𝒊𝒖𝒎 = = ( )
𝟒𝝅 𝜺𝒓 𝜺𝟎 𝒓𝟐 𝜺𝒓 𝟒𝝅 𝜺𝟎 𝒓𝟐
𝑭𝒂𝒊𝒓
𝑭𝒎𝒆𝒅𝒊𝒖𝒎 =
𝜺𝒓
