Electricity-Notes

  Current:

       I = Q/t, Where I = Current

                                    Q = Net charge flowing.

                                    t = time

                •  Unit:

                     The unit of current is Ampere.

                     Q = Coulomb(C)

                     I = Ampere(A)

                     t = Second(s) 1 A = 1C/1s

  Potential Difference:

       The potential difference between two separate points is defined as the work done to move a unit positive charge from one point to another.

       V = W/Q

                •  Unit:

                    The unit of potential difference is Volt

                    1 Volt = 1 Joule/ 1 Coulomb

  Ohm’s Law:

       Current ∝ potential difference

       V ∝ I

       V = I R where, R = Resistance

                •  Unit:

                     R = Ω(Ohm)

                     1Ω = 1V / 1 A

                •  Factors on which resistance depends:

                          ○  R ∝ 1, when A and material constant l = length

                          ○  R ∝ 1/ A, when l and material constant A = perpendicular cross-section

                              R ∝l / A,

                              R = ρl / A, where ρ = resistivity

                •  Resistivity: Resistivity of a substance is equal to the resistance of a unit square of that substance.

                     Its Unitis Ωm.

  Resistance in a series connection:

                     R = R1 + R2 + R3 + … + Rn

                     

  Resistance in parallel:

                     

  Heating Effect of current:

                     Electric energy = VIt

                     Heat, H = VIt = I²Rt

                •  Application:

                     Electric iron, toaster, fused wire, etc.

  Electric power:

                     P = VI = I²R = V²/ R

                •  Unit: 1 kWh = 3.6 × 10⁶J

                     1 W = 1V × 1A

  Ohm’ law: Under constant physical conditions (i.e., constant temperature, pressure etc.), the current flowing through a conductor is directly proportional to the potential difference across the conductor.

  Potential difference (which is measured in Voltage) is the cause of current (which is measured in Ampere).

  In conductors, flow of electrons constitute current. In a circuit current flow from positive terminal of the battery to the negative terminal, but electrons travels from negative terminal to the positive terminal. The negative terminal of a battery is said to be at lower potential and the positive terminal is said to be at higher potential.

  When a battery is not connected to any circuit, the potential difference across the terminals of the battery is equal to the EMF of the battery. (EMF = Electro Motive Force). Electromotive force, also called EMF, (denoted and measured in volts), refers to voltage generated by a battery or by the magnetic forceaccording to Faraday's Law, which states that a time varying magnetic field will induce an electric current.