· The current, I flowing in a conductor I = dQ/dt ,where dQ is the charge that flows through a cross-section in a time interval dt. SI unit of current is ampere (A). 1A = 1 C s-1.
· The current density J in a conductor is the current flowing per unit area. J = /AI
· Current is a scalar but current density is a vector.
· The general form of Ohm’s law
· Practical form of Ohm’s law states that V ∝ I, or V = IR where I is the current.
· The resistance R of a conductor is R = V/I . SI unit of resistance is ohm (Ω) and 1 Ω = 1V/1A
· The resistance of a material R = ρ l/A where l is length of the material and A is the area of cross section.The resistivity of a material determines how much resistance it offers to the flow of current.
· The equivalent resistance (RS) of several resistances (R1, R2, R3……..) connected in series combination is RS = (R1+R2 +R3……..)
· The equivalent resistance (RP) of several resistances (R1, R2, R3……..) connected in parallel combination is 1/RP = 1/R1 + 1/R2 + 1/R3 ………………,
· Kirchoff’s first rule (Current rule or junction rule): The algebraic sum of the currents at any junction is zero.
· Kirchoff’s second rule (Voltage rule or loop rule): In a closed circuit the algebraic sum of the products of the current and resistance of each part of the circuit is equal to the total emf included in the circuit.
· Electric power is the rate at which energy is transformed.
· If a current I flows across a potential difference V, the power delivered to the circuit is P = IV.
· In a resistor R, the electrical power converted to heat is P = I2R =V2/R
· The energy equivalent of one kilowatt-hour (kWh) is 1kWh = 3.6 X 106 J.
· Metre bridge is one form of Wheatstone’s bridge.
· Potentiometer is used to compare potential differences.
· Joule’s law of heating is H = VIt (or) H = I2Rt.
· Thermoelectric effect: Conversion of temperature differences into electrical voltage and vice versa.