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Tips to Score good in Electricity
- The force with which two charges interact is not changed by the presence of the other charges.
- Net force on any charge F=F1+F2+F3+F4+.....
- Electric field lines extend away from the positive charge and towards thge negative charges.
- Electric field produces the force so if a charge q is placed in the electric field E the force experience by the charge is F=qE
- Principle of superposition also applies to electric field
so E=E1+E2+E3+E4+......
- E is the electric field present due to all charges in the system not just the charge inside in the Gauss law.
- Flux crossing a closed surface does not depend on the shapes and size of gaussian surface.
- ∫E.dl over closed path is zero.
- Electric Potential is scalar quantity.
- Potential at point due to system of charges will be obtained by the summation of potential of each charge at that point V=V1+V2+V3+V4
- Electric forces are conservative force so workdone by the electric force between two point is independent of the path taken
V2-V1=-∫ E.dr
In cartesion coordinates system
E=Exi+Eyj+Ezk
dr=dxi+dyj+dzk
Now
dV=-E.dr
So,dv=-(Exdx+Eydy+Ezdz)
So, Ex=∂V/∂x
Similary,
Ey=∂V/∂y and Ez=∂V/∂z
Also
E=-[(∂V/∂x)i+(∂V/∂y)j+(∂V/∂z)k]
- Surface where electric potential is same everywhere is call equipotential surface
- Electric field components parallel to equipotential surface is always zero
- Electric potential in the spherical charge conductor is Q/4πεR where R is the radius of the shell and the potential is same everywhere in the conductor
- Conductor surface is a equipotential surface
- E=0 inside the conducter
- All charge resides on the outer surface of the conducter
- Electric at the surface is Perpendicular to the surface
Some userful Formula
Electric field intensity due to point charge
E=(KQ/r2)r
Where r is the distance from the point charge and r is the unit vector along the direction from source to point.
Electric field for the Uniformly charged ring
E=KQx/(r2+x2)3/2
Where x is the distance from the center of the ring
At x=0
E=0
Electric Field due to uniformly charged disc
E=(σ/2ε0)(1- x/(√R2+x2)
σ=Surface charge density of the disc
At x=0
E=σ/2ε0
Electric Field Intensity due to Infinite sheet of the charge
E=σ/2ε0
σ=Surface charge density of the sheet
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