^Power transferred theorem
Power transferred theorem
The power transferred by a cell to the load is maximum when R = r & given by
Also then 
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^Series combination of resistors
Series combination of resistors
The current across each circuit element is same, but potential difference is different & proportional to resistance of that part.
i.e. I = I1 = I2 = I3 & V1 = IR1, V2 = IR2, V3 = IR3 & R series = R1 + R2 + R3
^Electric resistance
Electric resistance
Depends upon the nature of material, shape & size, physical state like temperature, pressure, type & extent of impurity etc. of conductor. However r depends upon all above factors except on shape & size.
^Series dielectrics in a capacitor
Series dielectrics in a capacitor
If three dielectric slabs of thickness t1, t2 & t3, dielectric constants K1, K2 & K3 are placed between the plates of a parallel plate capacitor as shown, then the combination behaves as different dielectrics dividing the spacing are considered as capacitors connected in series.
Capacitance of this is given by
^Energy (potential) stored in a capacitor
Energy (potential) stored in a capacitor
A charged capacitor of any shape or size stores energy (potential) in the form of electrostatic electric field, it is given by
Energy per unit volume is called energy density, it is Electric energy density,
^What is a ratio?
^What is a ratio?
If a physical quantity can be completely described just by knowing its only numerical value, no unit & direction is required, then it is called ratio.
e.g. Strain, Poisson’s ratio, refractive index, relative density, relative permittivity, relative permeability, fine structure constant etc.
*A quantity having dimensions must posses some units, where as dimensionless quantity can have units. e.g. angle.
Facts
- *A quantity having dimensions must posses some units, where as dimensionless quantity can have units. e.g. angle.
Relative velocity have same dimensions as that of velocity where as relative density is dimensionless.
^Parallel plates with different charges
Parallel plates with different charges
If the two parallel metal plates X & Y having charge q1 & q2 are placed close to each other. Let the medium between the plates is air or vacuum. then in order to make net electric field in each plate zero, charges redistribute such that inner faces have equal & opposite charges & extreme faces have equal & of same sign as shown below
Elec. field on the left side (L) of plates, right side of plate (R) & between the plates due to the charge on face a, b, c & d is
^Field due to sheets
Field due to sheets
Using Gauss law we can prove that electric field sheets of charge density σ
1. 
near a infinite sheet or thick sheet
2. 
near a finite sheet or thin sheet
^Rules for writing units
^Rules for writing units
- The initial letter of a unit symbol named after a scientist is written in capital letters, however the full name begins with small letter. e.g. five newtons should be written as 5 N or 5 newtons but not as 5 n.
- Symbols for various units are never used in plural form. e.g. 5 N should be written as 5 N and not as 5 Ns, however we can write 5 newtons but not 5 Newtons.
- Symbols are never followed by a full stop.
- Not more than one solidus is used. e.g. Nm– 2s– 1 shouldn’t be written as N/m2 /s.
- The use of double prefix is avoided, when single prefix is available. e.g. instead of writing μμN we should write pN.
In calculations the prefix is attached with the numerator and not with the denominator.
