# NCERT Electric Charge and Fields

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Chapter 1: NCERT Electric Charge and Fields Easy NCERT Electric Charge and Fields Notes; Electric charges; Conservation of charges, Coulomb’s law-force between 2 point chargers, Electric field, Electric field due to point charge, Electric Field lines, Electric Dipole, Dipole moment.

## Electric Charge

Charge is the property associate with matter due to which it produces and experiences electric and magnetic effect.

Benjamin Franklin introduces 2 varieties of charges specifically charge and charge supported resistance electricity created by rubbing 2 not like objects like amber and wood.

### Conductors and Insulators

Those substance which readily allow the passage of electricity though them are called conductors.

The earth and people substances which provide high resistance to the passage of electricity square measure known as insulators.

### Conservation of Charge

The full charge of associate isolated system is often preserved, i.e. initial and final charge of the system will be the same.

## Chapter 1: NCERT Electric Charges and Fields

### Quantisation of charge

Charge exists in separate quantity instead of continuous worth and hence, quantised.

Mathematically, charge on an object, q= ± ne

where, n is an interger and e is electronic charge.

When any physical amount exists in separate packets instead of in continuous quantity, the number is alleged to be quantised.

Hence, charge quantised.

Unit of charge

1. SI unit coulomb (C)
2. CGS system
• Electrostatic unit, esu of charge or stat-coulomb (stat-C)
• electromagnetic unit, emu of charge or ab-C (ab-coulomb)

1 ab-C = 10C, 1 C = 3 -109 stat – C

### Coulomb ‘s Law

It states that electrostatic force of interaction acting between two stationary point charges is given by

### $F=\frac { 1 }{ 4\pi \varepsilon _{ 0 } } \cdot \frac { { q }_{ 1 }{ q }_{ 2 } }{ { r }^{ 2 } }$

where, q1 and q2 are  the stationary point charges and r is that the separation between them in air or vacuum.

Also,

### $\frac { 1 }{ 4\pi \varepsilon _{ 0 } } =\quad 9\quad \times \quad { 10 }^{ 9 }\quad N-{ m }^{ 2 }/{ C }^{ 2 }$

where, $\varepsilon_{0}$= permittivity of free space=8.85419×10-12 C2 /N-m2

The force between two charges q1 and q2 located at a distance r in a medium other than free space may be expressed as

### $F=\frac { 1 }{ 4\pi \varepsilon } \cdot \frac { { q }_{ 1 }{ q }_{ 2 } }{ { r }^{ 2 } }$

where, $\varepsilon$ is absolute permittivity of the medium.

Now,

### $\frac { { F }_{ vacuum } }{ F } =\frac { \frac { 1 }{ 4\pi \varepsilon _{ 0 } } \cdot \frac { { q }_{ 1 }{ q }_{ 2 } }{ { r }^{ 2 } } }{ \frac { 1 }{ 4\pi \varepsilon } \cdot \frac { { q }_{ 1 }{ q }_{ 2 } }{ { r }^{ 2 } } } =\frac { \varepsilon }{ { \varepsilon }_{ 0 } } ={ \varepsilon }_{ r }$

where $\varepsilon_{r}$ is called relative permittivity of the medium also called dielectric constant of the medium.

### Electric field

The electric field due to a charz Q at a point in space may be defined as the force that a unit +ve charge would experience if placed at that point.

### Intensity of electric field

The Electric field intensity (E) at any point due to a source charge is defined as the force (F) experienced per unit positive test charge (q0) at that point.

Electric field intensity is a vector quantity.

Its SI unit is newton/coulomb or volt/meter and dimensional formula is [MLT-3A-1].

### Electric field lines

Electric field lines are a way of pictorially mapping the electric field around the configuration of charge(s).

These lines start on +ve charge and end on -ve charge.

### Electric dipole

An Electric dipole is a system formed by two equal and opposite point charges planes at a minimum distance apart.

### Electric dipole moment

The product of magnitude of either charges and distance between two charges is called electric dipole moment.

Let q is the magnitude of either charge of electric dipole and d is  distance between the two charges then electric dipole moment,

### $p = q \cdot d$

It is a vector quantity and its SI unit is coulomb-meter.

### Electric flux

Electric flux linked with any surface is defined as the total number of electric field lines that are normally passes through that surface.

Total electric flux is over the whole surface S due to an electric field E,

### $\phi =\underset { s }{ \oint { E } } \cdot dS=\underset { s }{ \oint { E } } dS\quad cos \theta$

It is a scaler quantity. SI unit of electric flux is N-m2C-1 or V-m.

Dimensional formula of electric flux is [ML3T-3A-1]

### Gaussian Surface

It is a close to surface in 3-dimensional, through which electric flux can be calculated by applying surface integral.

### Gauss Theorem

It states that, the electric flux through any close the surface is equal to the 1/E  times the net charge (q) enclosed by the surfaces.