ELECTRICAL TECHNOLOGY

By:MOHD SHAHAROM IDRISJKE, PTSSELECTRICAL TECHNOLOGYET101UNIT ASSOCIATED WITH BASIC ELECTRICAL QUANTITIESWhat do we covered in this unit?SI units, Charges, Force, Work, Power, Electrical Potential and e.m.f, Resistance and conductance, Electrical power and energy, Summary of terms, unit and their symbols.SI UnitDefinition : SI unit is the modern form of themetric systemand is generally a system ofunits of measurementdevised around sevenbase unitsand the convenience of the number ten.

Scientific notation to represent quantities.Scientific notation also known asstandard formor asexponential notation, is a way of writing numbers that accommodates values too large or small to be conveniently written in standard decimal notation.

In scientific notation all numbers are written like this:a10bHow can we use it? Convert this,1000m = ?

Therefore, 103 is kilo. The symbol for kilo is k.Thats why, we can understand 1kilometer is 1km.1kilometerIn scientific notation, we write it like this,1 x 103 m

Do thisWhat is129km in scientific notation.24 x 104 m in km3.3 x104V in kV.250GB in scientific notation.250mA represent by..

Unit of chargeCoulomb -C (unit for electric charge)The standard unit of quantity in electrical measurements. It is the quantity of electricity conveyed in one second by the current produced by an electro-motive force of one volt acting in a circuit having a resistance of one ohm, or the quantity transferred by one ampere in one second.

Q=It

Unit of work or energy (J)Unit of work or energy is Joule (J).Where one joule is one newton meter. It is define as the work done or energy transferred when a force of one newton is exerted through a distance of one metre in the direction of the force.

W=FsF is the force in newton. S is the distance in meter moved by the body in the direction of the forceUnit of powerUnit of power is Watt (W).One watt is one joule per second. Power is defined as the rate of doing work or transferring energy.

P= W tW is the work done or energy transferred in joules and t is time in second.Electromotive Force -emfThe emf represents energy per unit charge (voltage) which has been made available by the generating mechanism and is not a "force".

e.m.f (electromotive force) or electrical potentialElectromotive Force is the energy supplied by a source of electric power in driving a unit charge around the circuit. The unit is the volt.

A difference in charge between two points in a material can be created by an external energy source such as a battery. This causes electrons to move so that there is an excess of electrons at one point and a deficiency of electrons at a second point. This difference in charge is stored as electrical potential energy known as emf. It is the emf that causes a current to flow through a circuit.

volts = watt = joules/second = joules amperes amperesampere seconds= joules coulombsResistanceThe opposition of a body or substance to current passing through it, resulting in a change of electrical energy into heat or another form of energy.

Unit for resistance is Ohm.Symbol for Ohm is .Symbol for resistance is R.

CurrentThe time rate of flow of electric charge.Electrical current is a measure of the amount of electrical charge transferred per unit time

Unit for current is Ampere or Amp.Symbol for current is I.ConductanceConductance is an expression of the ease with which electric currentflows through a substance. In equations, conductance is symbolized by the uppercase letterG. The standard unit of conductance is thesiemens(abbreviated S), formerly known as themho.

G= 1 / RElectrical PowerWhen a direct current of I amperes is flowing in an electric circuit and the voltage across the circuit is V volts, then power, in watts, P=IVElectrical energyElectrical energy = Power x time= VIt Joules.

Although the unit of energy is the joule, when dealing with large amounts of energy, the unit used is the kilowatt hour (kWh) where

1kWh= 1000 watt hour.= 1000 x 3600 watt seconds or joules= 3 600 000 J. SummaryQuantityQuantity Symbol Unit Unit SymbolLength lmeter mMassm kilogram kgTimetsecond sVelocityvmeter per second m/sAccelerationa meter per second squared m/s-2Electrical chargeQcoulomb CResistanceRohm ConductanceGsiemen SElectromotive forceEvoltVPotential DifferenceVvoltVWorkWjouleJEnergyE or Wjoule JPowerPwattWExercise1. If a current of 5 A ows for 2 minutes, nd the quantity of electricity transferred.2. A portable machine requires a force of 200N to moveit. How much work is done if the machine is moved 20 m and whataverage power is utilized if the movement takes 25 s?3. A mass of 1000 kg is raised through a height of 10 m in 20 s. What is(a) the work done (b) the power developed

4. Find the conductance of a conductor of resistance(a) 10, (b) 5 kand (c) 100 m?5. A source e.m.f. of 5 V supplies a current of 3 A for 10 minutes. How much energy is provided in this time?6. An electric heater consumes 1.8 MJ when connectedto a 250V supply for 30minutes. Find the power rating of theheater and the current taken from the supply?

Answer1. Quantity of electricity Q=ItcoulombsI=5 A,t=2x 60=120 sHence, Q=5x120=600C2. Work done=force xdistance=200 Nx20 m=4000 Nm or 4 kJPower=work done = 4000 J = 160 Js =160W time taken 25 s

3. (a)Work done=force xdistance and force = mass xaccelerationHence, work done= (1000 kgx9.81 m/s2)x (10 m) =98100 Nm= 98.1 kNm or 98.1 kJ(b) Power= work done = 98100 J=4905J/s =4905W= 4.905 kW time taken 20 s4.

5. Energy = power x time and power = voltage x powerhence, Energy = VIt = 5 x 3 (10x 60)= 9000Ws or J. = 9kJ.6. Power rating of heater is (1.8 x 106 )/(60x30) = 1kW.

Power, P= IV, thus I= P / V ,I= 1kW / 250V = 4A.ishaharom.blogspot.com

MSI 2010