ELECTROSTATICS
1. Electric
charge is a scalar quantity.
2. S.I. unit
of electric charge is coulomb.
3. Charge of
electron (e) = 1.6x10-19 coulomb
4. Positive
charge Negative
charge
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5. q = ne
Here q = electric charge
n = 0, ±1, ±2, ………….
e = 1.6 x10-19
6. F = 1/4πϵ0 (q1q2/r2)
Here 1/4πϵ0 = Coulomb’s
Constant = 9 x 109 NM2/C2
ϵ0 = Permittivity of free
space = 8.854 x 10-12 C2/NM2
q1 = Charge
q2 = Charge
r = Distance between two charges
7. 1 Coulomb = 3 x109 Stat
Coulomb
8. 1 Coulomb = 1/10 ab Coulomb
9. 1 ab Coulomb = 3 x 1010
Stat Coulomb
10. ϵr = ϵ/ϵ0
Here ϵr = Relative Permittivity
ϵ = Permittivity of medium
ϵ0 = Permittivity of
free space
11. Relative permittivity is unitless
and dimensionless.
12. Surface charge density = Q /
S
13. Linear charge Density = Q /
L
14. Volume Charge Density = Q /
V
15. E = F/Q
Here E = Electric field intensity /
Electric field strength
F = Force
Q = Charge
16.
E = 1/4πϵ0 (q/r2)
17. E
α 1/r2
E
r
18. P = q x 2a
Here q = charge
2a = Dipole length
P = Dipole Moment
19. Dipole moment is a vector
quantity. Its direction is along the dipole axis from –q to +q.
20. Ideal electric dipole is the dipole which
size 2a 0 and charge q ∞.
21. E axial = 1/4πϵ0 (2P/r3)
22. E equatorial = 1/4πϵ0
(P/r3)
23. E axial / E equatorial
= 2
24. Torque( τ ) = P x E = PE sin ᴓ
25. The electric lines of force start
from positive charge and ends on negative charge.
26. Two lines of force never cross
each other.
27. The lines of force have a tendency
to contract lengthwise. This explains attraction between two unlike charges.
28. The lines of force have a tendency
to expand laterally. This explains repulsion between two similar charges.
29. The lines of force do not pass
through a conductor because the electric field inside a charged conductor is
zero.
30. One unit positive charge gives 4π
lines of force.
31. Electric flux (φ) = ES cos ᴓ = E.S
Here E = Electric Flux
S = Area vector
32. Electric flux is a scalar
quantity.
33. Gauss’s Law- It states that for
any distribution of charges, the total electric flux linked through a closed
surface is 1/ ϵ0 times the total electric charge enclosed by closed
surface.
φE = q/
ϵ0
Here φE = Electric flux
q = Electric charge
ϵ0 = Permittivity of free
space
34. Electric
field due to a uniformly charged thin spherical shell-
E outside = 1/4πϵ0 (q/r2)
E inside = 0
E surface = σ/ ϵ0
35. Limitation of Coulomb’s law –
·
It
is valid only for point charges.
·
It
is a central force.
·
It
holds very good up to very small and very large distances (10-13m).
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