ch 1- Electric Charges and Fields

What happened if glass rod is rubbed with silk?

glass rod attains positive charge and silk attains a negative charge

properties of charge

like charges attract

unlike charges repel

Body which loses electron gets positively charged

Body which gains electron gets negatively charged

additivity of charges

Conservation of charge- total charge of a isolated system remains conserved

quanisation of charge- electric charge is always an integral multiple of e

q=±ne n=1,2,…. e=1.6×10^-19 C

Gold Lead Electroscope

detect charge on a body

Coulomb’s law/ Inverse square law

Electrostatic force between two stationary point charges is directly propertional to the product of magnitude of the charges and inversely proportional to the square of the distance between them.

ε₀

8.854×10^-12 C²N^-1m^-2

1/(4πε₀)

9×10⁹ Nm²C^-2

For dielectric constant

ε=ε₀×ε_r

superposition principle

the total force acting on a charge is equal to the vector sum of forces acting on the charge due to individual charges.

Electric Field

unit- N/C

Electric Field Strength/ Electric Field Intensity

electric field on +ve and -ve charges

Electric Field Lines

is a path straight line or curve through which an imaginary +ve charge moves if free to do so and the tangent to it at each point give the direct of the field at that point.

Field lines for unlike charges and like charges

Properties of Electric Field lines

• No two field lines never intersect (two directions for electric not possible at the same point)

• No. of field lines orginating or terminating increases with increase in magnitude of charge

• tangent to the field lines give the direction of the field at that point

• for +ve charge field lines are radially outward

• for -ve charge field lines are radially inward

• field lines originate from +ve charge and terminate at -ve charge

Electric flux

Total no. of electric field lines passing normally through a surface.

unit- Nm²/C or Nm²C^-1

Electric Dipole

Charge densities

Gauss’s Law

Total electric flux over a closed surface enclosing a charge is equal to,

electric dipole axial

electric dipole equitorial

field due to infinitely long wire

field due to infinitely long plane sheet

variation of electric field due to uniformly charged shell of radius R with distance r from center of the shell