ELECTROSTATIC POTENTIAL Flashcards

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1
Q

CAPACITANCE
AND SI UNIT

MATHEMATICALLY

A

RATIO OF ELECTRIC CHARGE TO THE POTENTIAL PRODUCED DUE TO THAT CHARGE

COULOMB/VOLT = FARAD

c= q/v

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2
Q

1 FARAD

A

THE CAPACITANCE OF A CONDUCTOR IS SAID TO BE 1 FARAD IF 1 C of charge raise its potential 1 volt

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3
Q

capacitance of paralled plate capacitor

A

1.consider a parallel plate capacitor of plate separation d and area of cross section A

2.let the capacitore be charged by CELL

  1. charge density
  2. the V potential between them
  3. since C= q/v

AE0/d

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4
Q

DIELECTRIC BREAKDOWN

A

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

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5
Q

WHY IS high potential difference not PREFFERED

A

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

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6
Q

CAPACITANCE of Insulated Spherical Conductor

noneedofchargedensity

A
  1. consider an insulated spherical conductor of radius ‘r’
  2. let a charge +q be given to it. this charge spread uniformly over the entire surface
  3. suppose the whole charge +q be present at the cente of sphere
    the potential V= kq/r
  4. if C is the capacitance
    ** c= 4πεor**
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7
Q

energy stored in a CAPACITOR

A

1/2 CV^2

OR
1/2 q^2/C

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8
Q

energy density of CAPACITOR

E.D = Energy/ volume

A

1/2 εo E^2

energy =1/2 CV^2
volume - A d
C= AE0/d
V= E d

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9
Q

DIELECTRIC

A

Insulating material which transmit ELECTRIC EFFECT

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10
Q

2 TYPES of dielectric materials

A
  1. non polar dielectrics: H2, N2. O2. CO2
    in such molecules centre of positive coincides with centre of negative charge
  2. 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
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11
Q

how DOES THESE DEPEND ON CAPACITANCE:
1. charge stored(q)
2. Voltage (V)
3. E.F
4. Area
5. distance
6. permittivity (E0)

A
  1. doesnt
  2. doesnt
  3. doesnt
  4. directly
  5. inversely
  6. directly
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12
Q

what happens to NON-polar DIELECTRIC when it is held in External ELectric field

e.g H2, N2, O2, CO2

urglasses😎

A

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

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13
Q

what happens to polar DIELECTRIC when it is held in External ELectric field

H2O, NH3. HCl

😎😎

A

ALL molecules will reorient and tend to align themselves in the direction of External Electric Field
and hence get polarised

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14
Q

Capacitance of Capacitor when DIELECTRIC SLAB OF thickness t=d and dielectric constant k is INTRODUCED

dontaddd

🦎

A
  1. CONSIDER c- capacitance of capacitor
    A- area
    d - distance btwn plates
    Eo - electric field
    Vo - potential difference
  2. when DIELECTRIC SLAB OF thickness t=d and dielectric constant k is INTRODUCED the slab gets polarised
  3. Electric field Ep is developed in dielectric region
  4. the net potential
    V=Vp= Ept = Eo t /k
    qt/AE0K
  5. C= AEoK/d
  6. C= K Co

Co is the capacitance when air is present between plates

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15
Q

Capacitance of Capacitor when DIELECTRIC SLAB OF thickness t<d and dielectric constant k is INTRODUCED

A
  1. CONSIDER c- capacitance of capacitor
    A- area
    d - distance btwn plates
    Eo - electric field
    Vo - potential difference
  2. when DIELECTRIC SLAB OF thickness t<d and dielectric constant k is INTRODUCED the slab gets polarised
  3. Electric field Ep is developed in dielectric region which is less than Eo
  4. therfore the net V between capacitor plate is
    V =Vo+ Vp
    Eo(d-t) + Ep t

5. C= EoA/(d-t) + t/k

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16
Q

Capacitance of Capacitor when CONDUCTING SLAB OF thickness t<d is introduced

A
  1. consider a capacitor of capacitance ‘C’ and area ‘A’. let ‘d’ be the separation between the plates
  2. let the capacitor be charged by using a cell
  3. the capacitance of capacitor is:
    Co = AEo/d
  4. suppose a conducting slab of AREA A AND thickness t<d is introduced btwn plates
    then V =Eo(d-t) + o

5, C = A Eo/ (d-t)
= Co / (1-t/d)

if t=d then C= infinity

17
Q

PARALLEL COMBINATION
ceff is
potential is
charge is

A

CEFF: C1+ C2

potential is same

charge is different
q1 = C1 V
q2 = C 2 V

18
Q

derive for parallel combo

POTENTIAL SAME😭

A
  1. consider three capacitors of capacitance C1, C2, C3 all connected parallel
    2.if q1,q2 and q3 are charges on each capacitor and V be the potential difference across PARALLEL combo
    then q = q1 +q2+ q3
    Ceq V = C1V +C2V +C3V
    Ceq = C1+ C2 + C3

CAPACITANCE INCREASES

19
Q

SERIES COMBINATION
ceff is
potential is
charge is

A

1/Ceq = 1/C1 +1/C2
different
same

20
Q

derive for SERIES COMBO

A
  1. consider 3 capacitors of capacitance C1, C2, C3 cinnected in series
  2. if V1, V2, V3 are the potential difference across each capacitor then V be the total potential across the capacitors
  3. V= V1+V2+ V3
  4. q/Ceq = q/C1+q/C2+ q/C3
  5. 1/ Ceq =1/C1 + 1/C2 +1/C3

CAPACITANCE DECREASES

21
Q

COMMON POTENTIAL
total charge before sharing
total charge after sharing

A

V = C1V1+ C2V2/ C1+ C2
* C1V1 +C2V2
* (C1+C2)V

22
Q

WHEN CHARGES ARE SHARED THERE IS ALWAYS OF ENERGY
ΔU = Ui - Uf

A
  • total energy before sharing= Ui= 1/2 C1V1^2 + 1/2 C1V2^2
  • total energy after sharing= Uf= 1/2 (C1+C2)V^2
  • ΔU =1/2 C1V1^2 + 1/2 C1V2^2 - 1/2 (C1+C2)V^2
  • =** C1C2(V1 - V2)^2 /2 (C1+C2)**

positive quantity. there is always some energy loss

23
Q
  • inside a conductor Electrostatic field is
  • at surface electrostaic field is
  • potential difference inside a conductor
  • potential difference on surface of conductor

be smarter😪

thus surface of conductor an equipotential SURFACE IN E FIELD

A
  • 0
  • normal to the surface
  • 0
  • 0
24
Q

ELECRTOSTATIC SHIELDING 🛡

A

THE method / phenomena of protecting a certain region from ELECTRIC FIELD

REASON why it safe inside a car during⛈

25
Q

ELECTROSTATIC POTENTIAL DIFFERENCE

unit and dimension

A

Is the amount of work done in bringing a +ve test charge from A TO B very slowly along any path between the 2 points without changing K.E

SI UNIT: Nm/C VOLT
D{: [ML2T-3A-1]

26
Q

ELECTROSTATIC POTENTIAL DIFFERENCE
OF A UNIT CHARGE

A

Vb = Winfinty-b/ qo

V= k q/ r

when r= infinity V=0

27
Q

ELECTROSTATIC POTENTIAL DIFFERENCE
OF A system of charges

A

V= k (q1/r1 + q2/r2+ q3/r3 …..+ qn/rn )

28
Q

ELECTROSTATIC POTENTIAL DIFFERENCE
at a point due to ELECTRIC DIPOLE

A

V = K pcosθ/ r^2 - a^2 cos^2 θ

29
Q

ELECTROSTATIC POTENTIAL DIFFERENCE
at a point due to ELECTRIC DIPOLE

where point is at axial line

cosθ

A

V= k p