Chapter Three Electrical Concepts Components 1 Basic Units

Chapter Three Electrical Concepts & Components 1

Basic Units & Dimensions o o o Fundamental quantities are: Mass, Length, Time, Charge System of Units: MKS or SI units. MKS = meter, kilogram, second. The basic unit of charge is the coulomb. In MKS system uses the basic units or some designated power of ten of those units. 2

Basic Units & Dimensions All given non-SI units should be converted into SI units before solving a problem, this is done using a table of conversion factors. o Each of the basic units has a “dimension” associated with it regardless of whether SI or non-SI units are used to measure it. o All the quantities have a unique dimension which is a combination of the four basic dimensions. o All conversion factors must be dimensionless quantities. o 3

Energy & Power o o Law of conservation of energy: energy cannot be created or destroyed in non nuclear situation, but it may be converted into other forms of energy. The basic unit of energy in the SI system is the Joule. Power is the time rate at which energy is expended. Power=energy/time. The basic unit of power in British system is horse power, and in the SI system Watt. 4

Charge & Current o o o The electric charge on a single electron has a charge e= -1. 602 x 10 -19 C. Charge can neither be created nor destroyed. Electrical current: the amount of charge passing a given point in a fixed instant of time. I= q/t. 1 A(ampere) = is a one coulomb of charge passing in one second. Current is measured using an ammeter. 5

Voltage o o Coulombs law: gives the force exerted by one charge on another charge. Voltage: is the amount of energy required to bring a test charge up to specific point near another charge divided by the value of the test charge. 6

Voltage The voltage is measured in Volts. o Direct current or DC voltage means a voltage that does not vary with time. o Alternating current or AC voltage which means a voltage that varies sinusoidally in time, going through a positive & negative peak each cycle. o 7

Electrical Power & Energy o o Power = Voltage x Current (measured in Watt) 1 Watt = is the power when a voltage of one volt is across a device that has a current of one ampere flowing through it. 1 horse power = 1 hp = 746 W. Energy = power x time (measured in joules) 8

Passive Electric Components: 1. Passive: means that the device itself needs no external electrical power source in order to operate. (e. g. Resistor, capacitor, & Inductor) 2. Active: means that the device requires electrical power source in order to function. (e. g. vacuum tubes, transistor) 9

Resistor o Resistance is measured in ohms (Ω ). o o Ohms law: the voltage and the current in a given resistance are linearly related. V= I. R (R= resistance) P = V. I = V 2/R = I 2. R 10

Capacitor o o o Capacitor: is two conductors separated by dielectric material, which have a voltage difference between them & have charges of different polarities on the two conductor. C=Q/V Capacitance is measured in Farad (1 F is the capacitance of one coulomb of charge on each conductor with a voltage difference 1 V) 11

Capacitor o o Capacitor doesn’t provide a conducting path between the two plates. i. e. It blocks DC current. If the voltage across C is varying with time, time-varying current can be carried through C. 12

Inductor o o o A magnetic field is produced when a current flow through a wire. Magnetic flux: is the product of the area through which the magnetic field lines are flowing times the magnetic properties of the material (permeability). Inductance(measured in Henry): is the ratio of the total magnetic flux linked by the current producing it to the current. 13