electricity

• Electricity has an important place in modern society
• Electricity is a controllable and convenient form of energy for various uses in homes, schools, hospitals, and industries
• Electric current flows through a conductor when electric charge flows through it
• An electric circuit is a continuous and closed path for electric current to flow
• Electric current is the rate of flow of electric charges
• In metallic wire circuits, electrons constitute the flow of charges
• The direction of electric current is considered opposite to the direction of the flow of electrons, which are negative charges
• The SI unit of electric charge is coulomb (C)
• The SI unit of electric current is ampere (A)
• Small quantities of current are expressed in milliampere (mA) or microampere (μA)
• An ammeter measures electric current in a circuit and is connected in series
• Electric potential difference is the work done to move a unit charge from one point to another
• The SI unit of electric potential difference is volt (V)
• Potential difference is measured by a voltmeter connected in parallel
• Ohm's Law states that the potential difference across a conductor is directly proportional to the current flowing through it, provided its temperature remains the same
• Resistance (R) is the property of a conductor to resist the flow of charges
• The SI unit of resistance is ohm (Ω)
• Resistance of a conductor is 1 ohm when the current through it is 1 ampere
• Current through a resistor is inversely proportional to its resistance
• Variable resistance components are used to regulate current without changing the voltage source
• Rheostat is a device used in electric circuits to change the resistance
• Resistance of a conductor depends on its length, area of cross-section, and the material it is made of
• Resistance of a uniform metallic conductor is directly proportional to its length and inversely proportional to the area of cross-section
• Resistance of a conductor is given by R = ρ l A, where ρ is the electrical resistivity of the material
• Metals and alloys have low resistivity, while insulators have high resistivity
• Resistance and resistivity of a material vary with temperature
• Resistance of a wire is calculated using the formula ρ = (RA/l) = (R π d^2 / 4l)
• Resistance of a wire is halved when the length is doubled, and increased when a thicker wire of the same material and length is used
• Resistance of a wire of different material of the same length and area of cross-section changes
• Resistance of a wire depends on its length, area of cross-section, and the material it is made of
• Resistance of a system of resistors connected in series is the sum of the individual resistances
• Current is the same in every part of a series combination of resistors
• Potential difference across a series combination of resistors is denoted as V
• Total potential difference across a combination of resistors in series is equal to the sum of potential differences across the individual resistors: V = V1 + V2 + V3
• Current through a circuit with resistors in series is constant
• Equivalent resistance of resistors in series is the sum of their individual resistances: Rs = R1 + R2 + R3
• In a parallel circuit, total resistance is given by the reciprocal of the equivalent resistance: 1/Rp = 1/R1 + 1/R2 + 1/R3
• Total current in a parallel circuit is equal to the sum of the separate currents through each branch of the combination: I = I1 + I2 + I3
• Total resistance of parallel resistors is decreased compared to individual resistances
• Heating effect of electric current: Energy supplied to the circuit by the source is dissipated as heat in resistors