Introduction
Charge is something associated with matter due to which it produces and experiences electric and magnetic effects. The study of charges at rest is called static electricity or electrostatics while the study of charges in motion is called current electricity. There are two types of electric charge:
(i) Positive charge and (ii) Negative charge. The magnitude of elementary positive or negative charge is same and is equal to. \[1.6\times {{10}^{-19}}C\] Charge is a scalar quantity its SI unit is ampere second or coulomb.
- Basic Properties of Electric Charge
(1) Similar charges repel and opposite charges attract.
(2) A charged body attracts light uncharged bodies.
(3) Accelerated charge radiates energy.
- Conductors and Insulators
The materials which allow electric charge (or electricity) to flow freely through them are called conductors. Metals are very good conductors of electric charge. Silver, copper and aluminium are some of tile good conductors of electricity. The materials which do not allow electric charge to flow through them are called nonconductors or insulators. For example, most plastics, rubber, non-metals (except graphite), dry wood, wax, mica, porcelain, dry air etc., are insulators.
It states that, the electrostatic force of interaction (repulsion or attraction) between two electric charges \[{{q}_{1}}\] and \[{{q}_{2}}\]separated by a distance r, is directly proportional to the product of the charges and inversely proportional to the square of distance between them.
\[F\propto {{q}_{1}}{{q}_{2}}\] and \[F\propto 1/{{r}^{2}}\] or \[F=k\frac{{{q}_{1}}{{q}_{2}}}{{{r}^{2}}}\]
\[K=\frac{1}{4\pi {{\varepsilon }_{0}}}\]\[=9\times {{10}^{9}}\frac{N{{m}^{2}}}{cou{{l}^{2}}}\Rightarrow {{\varepsilon }_{0}}=8.85\times {{10}^{-12}}\frac{cou{{l}^{2}}}{N{{m}^{2}}}\]
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Electric Field
- Electric Field: The region surrounding an electric charge or a group of charges in which another charge experiences a force of attraction or repulsion is called 'electric field'. \[\overrightarrow{E}=\frac{\overrightarrow{F}}{{{q}_{0}}},\overrightarrow{E}=\underset{{{q}_{0}}\to 0}{\mathop{\lim }}\,\frac{\overrightarrow{F}}{{{q}_{0}}}\] The S.L unit of electric field intensity is N/coul or volt/metre.
- Electric Lines of Force
An electric line of force is that imaginary smooth curve drawn in an electric field along which a free isolated unit positive charge moves. Two lines offeree never intersect. If they are assumed to intersect, there will be two directions of electric field at the point of intersection, which is impossible.
- Electric Flux ((\[\phi \])
The total number of electric lines of force through a given area is called the electric flux.
(a) For open surface, \[{{\phi }_{0}}=\int{d\phi =\int{\overrightarrow{E}.d\overrightarrow{s}}}\]
(b) For closed surface, \[{{\phi }_{0}}=\oint{\overrightarrow{E}.d\overrightarrow{s}}\]
The total electric flux linked with a closed surface is \[\left( \frac{1}{{{\varepsilon }_{0}}} \right)\] times the charge enclosed by the closed surface (Gaussian surface), i.e. \[\oint{\overrightarrow{E}.d\overrightarrow{s}=\frac{q}{{{\varepsilon }_{0}}}}\]
Potential at a point can be physically interpreted as the work done by the field in displacing a unit + ve charge from some reference point to the given point.
i.e., \[V=\frac{w}{{{q}_{0}}}\]
\[V=-\int\limits_{\infty }^{r}{\overrightarrow{E}.d\overrightarrow{s}}\] i.e.
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Symbol of p-n junction diode
p-n junction under forward bias: When p-side is connected to positive terminal and n - side to negative terminal of external voltage, it is said to be forward biased.
The applied voltage V is opposite to build in Potential\[{{V}_{0}}\], hence depletion layer width decreases and barrier height is reduced to\[({{V}_{0}}-V)\]. There is minority carrier injection, hence charges begin to flow. Current is in the order of mA.
(c) p-n junction under reverse bias: When p-side of p-n junction is connected to -ve terminal more... 
