Synopsis

According to Drude and Lorentz, metals contain a large number of free electrons while the positive ions are fixed in their locations. When the conductor is in open the net charge moving along a conductor through any cross section is Zero. When the ends of the conductor are connected to the battery through a bulb the bulb glows.
If 'Q' is the charge crossing through any cross-section of the conductor in a time interval 't', then electric current $$I=\frac{Q}{t}$$ .A conductor with cross section is 'A' and V_d is the drift speed of the electron, $$ \eta $$ is the number of electrons then electric current I = nqAv_d, where q is the charge of an electron.

Potential is the work done by the electric force on unit positive charge to move it through a certain distance. The S.I unit of potential is "Volt".
1volt = 1 joule/coulomb.

Ohm's law is an empirical law which connects voltage and current. It states that "at constant temperature the current through the conductor (I) is directly proportional to voltage

difference between the ends of conductor". i.e. V a I or V = IR, where It' is the resistance. When resistors are connected in series them the effective resistance.

R_eq = R₁ + R₂ + R₃+.....................
When resistors are connected in parallel then the effective resistance is

$$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\frac{1}{R_4}........$$

To DC circuits there are two Kirchhoff s laws. 1) Junction law, 2) Loop law. Electric power can be calculate by the formula

$$P=I^2R=\frac{V^2}{R}$$