Electric Charges and Fields Flashcards
What is smallest unit of charge?
Stat coulomb also called franklin or esu (electrostatic unit)
1 coulomb = 3 multiply 10*9 stat coulomb
Largest unit of charge
Faraday
1 F = 96500 C
Proton, mass and charge
Mass = 1.67 • 10-27 kg
Charge = +1.6 • 10-19 C
Electron, mass and charge
Mass= 9.1 • 10-31 kg
Charge= 1.6 • 10-19C
Neutron, mass and charge
Mass= 1.67 •10*-27 kg
Charge=0
Is charge variant or invariant?
Charge, unlike mass is invariant, which means it does not change with time
m= m not / root 1- (v sq/c sq)
1 coulomb has charge of how many electrons
6.25 • 10^18 e = 1 C
Alpha particle, charge and mass
Charge = +2e
Mass = 4 p
Charge on deutron
+e ( because of one proton and removal of one electron)
Remove one electron to from deuterium to get deutron
Is positive ions conserved in nature?
No, total charge is
Formula for specific charge and SI uni
S = charge/mass or C/kg
Method of charging for insulators
Rubbing/friction
Glass rod (+) and silk (-)
Fur (+) and ebonite rod/rubber( -)
What is a sure test of electrification and magnetism?
Repulsion (can only happen when both charged)
Attraction can happen also if a body is neutral by induction
What is gold leaf electroscope used for?
Device to roughly estimate charge on body
What is Coulomb’s law and constant
F = k q1 q2/ r^2
k = 9 • 10^9 Nm^2/C^2
Which is stronger, electrostatic or gravitational force?
Electro, as gravitation is the weakest
1 Newton has how many dyne
10^5 dyne = 1 N
Formula, SI unit, value of permitivity
€not= 8.85 × 10⁻¹² F/m
Farad/m or C^2/Newton m^2
F= qq/4 pi €not r^2
Formula of dielectric constant and formula of force with it
Also denoted by k but different from coulomb constant
k = €/€not
medium/free space
Dielectric constant is infinity for and what does that mean for force
Conductors
F’=0 because F’ = F/K = F/infinity = 0
Where is null point for 2 like or similar charges and formula for this
Null point in between where its distance from smaller charge is x
x = r / (root n) +1
where r is distance between the 2 charges
And n= bada charge/ chhota charge
Where is null point for opposite charges and formula for it’s distance
Null point is to the side of both charges, not in between, with x distance from smaller charge
x = r/ (root n) - 1
Where r is the distance between 2 charges
And n is ration of big charge by smaller charge
2 vectors A and B at an angles, formula for resultant
R = underoot A^2 + B^2 + 2AB cos theta
If A=B then R= 2A cos (theta/2)
Resultant when A and A have 60 degree
(Root 3) A
Resultant when A and A have 90 degree
(Root 2) A
Resultant when A and A have 120 degree
R = A
Coulomb’s law in vector form
F cap = k q1 q2 (r vector/arrow) /r^3
As r vector= r • r cap
In 2 charges on pendulum repelling, the ratio of their tan theta is what
Tan theta 1/ tan theta 2 = m2/ m1
This is independent of charge
Formula for electric field strength/ electric field intensity. Definition and SI unit
F= kq/ r^2
Force experienced per unit POSITIVE test charge
SI is N/C or another unit V/m
Electric field due to circular arc
(2k lamda/r ) sin (alpha/2)
Electric field due to semi circular arc and infinite charged rod in x direction
2k lamda/r
O for charged rod in y direction
Electric field due to ring at an axis
kQx/ (x^2 + R^2) ^3/2
Where E max is at x = +- R/ root2
Electric field due to charged rod
E in x = k lamda/ r (sin alpha + sin beta)
E in y = k lamda / r (cos alpha - cos beta)
Electric field at axial point of rod with L length at a distance x
E = kQ/ r (r+L)
Force experienced by negative charge in electric field
F = -qE (F and E vector)
What are the equations of motion valid for motion of charged particle in electron field
v = u + at
s = ut + (1/2) at^2
v^2 = u^2 + 2as
s = [(u+v)/ 2] • t
Which of the following can’t be deflected by electric field?
1. X-ray
2. B particles
3. Proton
4. Alpha particles
5. Gamma rays
6. Neutron
X-ray, gamma ray and netron because they don’t have any charge
Beta have -1 charge
Electric dipole formula for p
p = qd
Coulomb metre
p and d are vectors
Electric field due to dipole at axial point, equatorial point, general point
2kp/r^3
-kp/ r^3
kp/r^3 • underoot 1+ 3 cos sq theta
Formula for torque on dipole in electric field
p E sin theta
Min for 0degree and 180 degree
Max for 90degree with torque=pE
Dipole oscillation formula for time period
T = 2 pi underoot I/ pE
T= 2pi/ omega
Omega = underoot pE/I
Electric flux formula
Fi = E A cos theta
Where A or area vector is perpendicular to surface
Gaus law formula
Integral of E • ds = fi = q enclosed/ €not
According to gaus law electric field in, on and out hollow sphere and solid sphere (non conducting)
Hollow or solid conducting sphere
E in = 0
E out = kQ/r^2
E on = kQ/R^2 = sigma/ €not
Solid non-conducting
E in = kQr/R^3
E out = kQ/r^2
E on = kQ/R^2
Electric field of infinite line or charge
E = 2k lamda/ r
Electric field of infinite non conducting sheet (cylindrical or cuboidal
E = sigma/ 2 € not
It is independent of r
Flux through a cube with charge at the centre, face centre, edge centre and corner
Flux when centre of cube = q/ € not
(Through each face q/ 6 € not)
Face centre = q/2 € not
Edge = q/ 4 € not
Corner = q/ 8 € not
