Electrostatics. Flashcards
What is charge q in terms of number of electrons e ?
q=ne
Coulumbs Law
F= k q1q2/ r^. k=1/4πε₀ unit of k = N metre square per coulomb square k= 9 x 10^9 ε₀= 8 x 10^-12
Unit of k in electrostatics Coulomb’s law
N m^ c^-2
Unit of ε₀ (permittivity of free space )
C^/N m^-2
Field strength due to a point charge
E= k q/r^
Direction of field strength due to positive and negative charge ?
Due to positive charge field strength is away from the charge and due to negative charge field strength is towards the charge.
Electric potential V due to point charge
V= k q/r
Electrostatic potential energy U of two point charges.
U= k q1q2/r
What is electrostatic potential energy in terms of charge and electrostatic potential ?
U= qV
Potential difference in an uniform electric field?
In an indoors electric field , potential difference V= Ed
Formula of electric dipole
p=q(2a). Direction of p vector is from -q to +q
Electric field strength E for a uniformly charged spherical shell
E(i)=0
E(s)=k q/R^= σ/ε₀
Eo= kq/r^
Electric field strength e for a solid sphere of charge.
E(i)=Kqr/R³
E(s)=Kq/R^
Eo=Kq/r^
Electric field strength E on the axis of a uniformly charged ring
E= Kqx÷(R²+x²)^3/2
At centre , x= 0 and hence E=0
Electric field Strength E for a infinitely long line charge
E= λ/2πε₀r
Electric potential V for a uniformly charged spherical shell
V(i) = V(s) = Kq/R=σR/ε₀
Vo=Kq/r
Electric Potential for a solid sphere of charge
V(i)= Kq÷R³(1.5 R² - 0.5 r²)
V(s)=Kq/R
Vo=Kq/r
Electric potential on the axis of a uniformly charged ring
V=Kq÷√R²+x²
At centre ,
x=0
V= Kq/R
Electric Potential V for an infinitely long line charge
PD= λ÷2πε₀ ln (r₂/r₁)
Torque due to an electric dipole when placed in an uniform electric field
Torque = pE sin #
Electric potential energy U due to an electric dipole when placed in a uniform electric field
U=-PE= -pE cos#
When an electric dipole is placed in an uniform electric field , what happens when #=0?
In #=0 , it’s a stable equilibrium position.
In this position , F=0
Torque =0
U=-p.E= minimum
When an electric dipole is placed in an uniform electric field , what happens when #=180?
=0 is unstable equilibrium position. In this F=0 and torque = 0 but U= +p.E= maximum.
Electric flux on surface formula ?
∫∞=∫E . dS
Mathematically , what is Gauss Law?
∫E . dS= q(in) / ε₀
or ‘Electric Flux from a closed surface’= q(in) / ε₀
Electric filed due to a plane sheet of charge
E=σ/2 ε₀
What is electric field on the surface of any charged conducting body ?
E=σ/ε₀
Electric filed of a conductor under electrostatic conditions?
E(i)= 0 E(s) = σ/ε₀
What are the two properties of a conductor regarding electric field lines and electric potential.
- On the surface of charged conductor electric lines are perpendicular to the surface
- The potential of charged conductor through out its volume is same.
Potential difference between two charged spherical shells
V1-V2=q1÷4πε₀(1/r1-1/r2)
What is charge per unit length λ?
It’s charge distribution along a line.
dq = λ dx
What is charge per unit area σ?
It’s charge distribution on the surface.
dq= σ dA
What is charge per unit volume p?
It’s charge distribution throughout a volume.
dq= p dV
