ELECTROSTATIC POTENTIAL Flashcards
CAPACITANCE
AND SI UNIT
MATHEMATICALLY
RATIO OF ELECTRIC CHARGE TO THE POTENTIAL PRODUCED DUE TO THAT CHARGE
COULOMB/VOLT = FARAD
c= q/v
1 FARAD
THE CAPACITANCE OF A CONDUCTOR IS SAID TO BE 1 FARAD IF 1 C of charge raise its potential 1 volt
capacitance of paralled plate capacitor
1.consider a parallel plate capacitor of plate separation d and area of cross section A
2.let the capacitore be charged by CELL
- charge density
- the V potential between them
- since C= q/v
AE0/d
DIELECTRIC BREAKDOWN
WHEN THE INSULATOR IS KEPT IN VERY HIGH ELECTRIC FIELD
THE OUTER e- MAY GET DETACHED FROM THEIR ATOMS
THE DIELECTRIC BEHAVES LIKE CONDUCTORS
THIS PHENOMENON IS DIELECTRIC BREAKDOWN
WHY IS high potential difference not PREFFERED
IF there is high voltage, there will be HIGH E.F
THIS might ionize the surrounding air and accelerate the charges to oppositively charged capacitor plates
therefore TOTAL CHARGE OF CAPACITOR DECREASES
CAPACITANCE of Insulated Spherical Conductor
noneedofchargedensity
- consider an insulated spherical conductor of radius ‘r’
- let a charge +q be given to it. this charge spread uniformly over the entire surface
- suppose the whole charge +q be present at the cente of sphere
the potential V= kq/r - if C is the capacitance
** c= 4πεor**
energy stored in a CAPACITOR
1/2 CV^2
OR
1/2 q^2/C
energy density of CAPACITOR
E.D = Energy/ volume
1/2 εo E^2
energy =1/2 CV^2
volume - A d
C= AE0/d
V= E d
DIELECTRIC
Insulating material which transmit ELECTRIC EFFECT
2 TYPES of dielectric materials
- non polar dielectrics: H2, N2. O2. CO2
in such molecules centre of positive coincides with centre of negative charge - polar dielectrics: H2O,NH3, HCl
* in such molecules the centre of positive and negative don’t coincide
- each molecule have permentant dipole
- in absence of Eext, the individual dipole moment tend to orient Randomly due to THERMAL AGITATION
- so the net DIPOLE MOMENT IS ZERO
how DOES THESE DEPEND ON CAPACITANCE:
1. charge stored(q)
2. Voltage (V)
3. E.F
4. Area
5. distance
6. permittivity (E0)
- doesnt
- doesnt
- doesnt
- directly
- inversely
- directly
what happens to NON-polar DIELECTRIC when it is held in External ELectric field
e.g H2, N2, O2, CO2
urglasses😎
the centre of +ve charge of each molecule is pulled toward -ve plate
this dipole is induced in each molecule & hence the dielectric is POLARISED
what happens to polar DIELECTRIC when it is held in External ELectric field
H2O, NH3. HCl
😎😎
ALL molecules will reorient and tend to align themselves in the direction of External Electric Field
and hence get polarised
Capacitance of Capacitor when DIELECTRIC SLAB OF thickness t=d and dielectric constant k is INTRODUCED
dontaddd
🦎
- CONSIDER c- capacitance of capacitor
A- area
d - distance btwn plates
Eo - electric field
Vo - potential difference - when DIELECTRIC SLAB OF thickness t=d and dielectric constant k is INTRODUCED the slab gets polarised
- Electric field Ep is developed in dielectric region
- the net potential
V=Vp= Ept = Eo t /k
qt/AE0K - C= AEoK/d
- C= K Co
Co is the capacitance when air is present between plates
Capacitance of Capacitor when DIELECTRIC SLAB OF thickness t<d and dielectric constant k is INTRODUCED
- CONSIDER c- capacitance of capacitor
A- area
d - distance btwn plates
Eo - electric field
Vo - potential difference - when DIELECTRIC SLAB OF thickness t<d and dielectric constant k is INTRODUCED the slab gets polarised
- Electric field Ep is developed in dielectric region which is less than Eo
- therfore the net V between capacitor plate is
V =Vo+ Vp
Eo(d-t) + Ep t
5. C= EoA/(d-t) + t/k