Download Electrical Engineering Concepts: Q&A for Exam Preparation and more Exams Electrical Engineering in PDF only on Docsity!
Atomic number - answer gives indication of number of orbiting electrons Where do excess electrons on - ve plate in battery go? - answer +ve plate Ρ - answer resistivity symbol Extra low voltage - answer below 50v a.c or 120v d.c Magnetic lines of force - answer can never touch each other Diode - answer has a cathode and anode Low voltage (a.c) - answer exceeding extra low voltage, but below 1000v between conductors, or 600v conductors to earth Low voltage (d.c) - answer below 1500v Stator - answer the stationary portion of an electric generator or motor Weight - answer a measure of the force which a body exerts in anything supporting it Mass - answer the measure of the amount of material in a substance Work done - answer force x distance Power - answer the rate at which work is done Impedance - answer resistance to flow of current When rearranging formula - answer the new subject must always be on the top line Atoms - answer bound by electrical force Molecules - answer bound by chemical force Charges - answer like charges repel and opposite charges attract Current flows from - answer negative to positive
Conventional current - answer positive to negative Charge is measured in what? - answer coulombs (c) Charge is - answer the follow of electrons in one direction E - answer electromotive force Joule - answer capacity to do work over a period of time Electrolyte - answer a chemical solution that contains many ions Old live one - answer red Old live 2 - answer yellow Old live 3 - answer blue Old neutral - answer black Phase 2 - answer black Phase 3 - answer grey Three main effects of electric current - answer heating, chemical, magnetism Candela - answer si unit for luminous intensity Kelvin - answer si unit for temperature Potential difference is measured in - answer volts Weber (wb) - answer si unit used to measure magnetic flux Tesla (t) - answer the unit for magnetic flux density When indices are negative ... - answer the result becomes a fraction e.g. 5 to power of - 1 = 1/ 5 to power of - 2 = 1/ Tera (t) - answer 10 to the power of 12 Giga (g) - answer 10 to the power of 9
1 joule = - answer 1 coulomb x 1 volt Where to connect ammeter in circuit - answer in series with the load Where to connect voltmeter in circuit - answer in parallel to the load Connecting wattmeter in circuit - answer connect so the meter is in parallel and series at once. Using ohmmeters in circuit - answer only when it's not on, and connect in parallel. Current flowing towards viewer - answer shown with a large dot Current flowing away from the viewer - answer shown with a cross Current direction when flowing towards viewer - answer it rotates anti clockwise Current direction flowing away from viewer - answer rotates clockwise The more current flowing - answer the stronger the magnetic field will be Solenoid - answer one long insulated conductor wound to form a coil. Causes magnetic fields to become stronger. Flow of current in a solenoid - answer north to south Dynamic induction - answer where a conductor moves and cuts a magnetic field, inducing an emf. Alternators - answer use rotating magnets to generate electricity Static induction - answer induction of a current into a circuit where no physical movement has taken place Mean voltage of a waveform - answer zero because half the cycle is positive and half is negative Finding rms value - answer each value is squared, then add the new values together and divided by the number of values. The square root of this answer is the rms. Peak to peak value - answer the measurement between the positive and negative peak on a cycle
Step-up transformer - answer more turns on the secondary stage, increases voltage Step-down transformer - answer more turns on the primary stage, decreases voltage 1kg in newton's - answer 9.81n Calculating power losses - answer output divided by input Class one lever - answer fulcrum (pivot point) is in the middle e.g. see saw Class three lever - answer pivot point (fulcrum) at one end with the load at the opposite end e.g. tweezers Class two lever - answer fulcrum is at one end with the load in the middle e.g. wheelbarrow Star symbol - answer y Delta symbol - answer δ Neutral in star - answer doesn't have to carry current unless different values of current being drawn by the phases. Works on an overflow principle. Power in delta configuration - answer 3 x that of star for same resistances Line current (il) for star - answer the current flowing through the line supplying each load Phase current (ip) for star - answer the current flowing through each load Line voltage (vl) - answer voltage between the line conductors Phase voltage (vp) - answer the voltage across any one load Line current (il) for delta - answer current flowing through the cable supplying each load Phase current (ip) for delta - answer the current flowing through each load Questions on 3 phase - answer square root the answer by 3 which is your 3 phases Relays and contactors work by - answer using a solenoid that works as an electrical switch
Transformer lamination - answer make up transformer cores, they are thin insulated slices of metal stacked on each other Eddy current - answer products of induction. Small rotating currents around the transformer core. Transformer laminations stop these as they waste energy through heat. Self inductance - answer where the transformer winding induces a magnetic field that limits current flow by flowing back into the winding. Mutual inductance - answer where a primary winding indices a magnetic field that induces a current into a second winding. Inductor - answer length of wire wound in a coil. Used to induce a magnetic field. Inductance symbol - answer l Unit of inductance - answer henry (h) Capacitor - answer two conducting electrodes of metal separated by an insulating material Purpose of capacitor - answer stores electric charge between two electrodes Symbol for capacitance - answer c Unit of capacitance - answer farad Impedance value - answer varies at different frequencies and is not the same as resistance despite being measured in ohms Root mean square - answer the square root of the mean of the squares of the values Lenz's law - answer the induced e.m.f is always in such a direction as to oppose the change that caused it. An atom with one electron missing is - answer positive Potential difference - answer change in energy levels measured across the load terminals Power = - answer mass x acceleration x velocity Oil cooling - answer common for large national grid transformers
Volt drop (series) - answer work our current for circuit (include all resistors) Work out voltage using the resistor you want and current Phase voltage - answer voltage between phase and neural (lower) Line voltage - answer voltage between two lines (higher) Transformers have more turns - answer on the higher voltage side Electrical force - answer force created by an electrical field Magnetic force - answer force created by a magnetic field Centripetal force - answer a force that causes an object to move in a circle Centrifugal force - answer acts away from the centre Shearing force - answer moves one face of a material over another Friction force - answer resists or prevents the movement of two surfaces in contact Compressive force - answer force pushing things together Tensile force - answer the force pulling things apart Cohesive or adhesive force - answer the force required to hold things together Inertial force - answer the force required to get things moving Work done = - answer force x distance Power = - answer work done / time taken Non ferrous - answer metals that don't contain iron Ammeter connection in circuit - answer both leads in front of resistor Voltmeter connection in circuit - answer one lead either side of resistor Like poles of a magnet - answer repel each other Unlike poles of a magnet - answer attract each other Relay - answer electro magnetic switch operated by a solenoid
Synchronous speed - answer the speed at which the magnetic field rotates Current in a combined resistive and capacitive circuit - answer leads the voltage by 90 degrees Role of magnetic core of transformers - answer to increase and concentrate the magnetic flux that links the primary and secondary coils Right hand grip thumb - answer points to north pole Right hand grip fingers - answer indicate current direction Alternators - answer use rotating magnets to generate electricity True power is measured in - answer watts Apparent power is measured in - answer va Reactive power is measured in - answer var Improve power factor in ac circuit by - answer fitting a capacitor in parallel with the load First finger on flemings left hand rule - answer magnetic field Second finger on flemings left hand rule - answer current Flemings left hand rule is for - answer electric motors Flemings right hand rule is for - answer generators Thumb on flemings right hand rule - answer motion First finger on flemings right hand rule - answer field Second finger on flemings right hand rule - answer current Commutator - answer used in generators to change ac to dc Periodic time - answer amount of time to complete one cycle Mean voltage of any half cycle - answer multiply peak voltage by 0. Work out rms voltage - answer multiply peak voltage by 0.
Rotor - answer moving part of a generator or motor Delta - answer windings of the transformer are in a circular formation. Delta voltage - answer voltage across each winding is the same as the line voltage because the start of each winding is connected to the end of another. Cast resin transformer - answer used where there is a fire risk in indoor situations Eddy current - answer produces heat which can cause loss of energy Hysteresis loss - answer transformer core becomes magnetised and de magnetised, costing energy to re magnetise Thermistor - answer accurately determines the temperature of the space Diode - answer only allows current to flow in one direction Diac - answer won't allow current flow unless a pre set voltage is reached Thyristor - answer allows current flow between two of its terminals if a small current is sensed on the third Scr - answer like a diode, with a gate terminal which activates the switch when a small current is sensed on that terminal Resistor - answer control or reduce current flow Thermistor - answer resistor which varies with temperature Photoresistor - answer a light sensitive resistor; the more light that shines on it, the more it resists so the less current there is Variable resistor/potentiometer - answer used to vary resistance in a circuit manually Capacitor structure - answer two terminal electrical component Capacitor use - answer stores energy electrostatically Capacitance of a capacitor - answer varied by the area of the plates and the size of the gaps between the plates the narrower a gap the higher the strength Rectifier - answer uses diodes to convert ac to dc Invertor - answer converts dc to ac
Capacitor in capacitor start motor - answer increases phase displacement Sinusoidal wave - answer a smooth periodic wave Frequency = - answer 1 / time (seconds) Half wave rectification - answer requires a diode in each phase/live Full wave retification - answer requires two diode and a centre tapped transformer, or four diodes in a bridge configuration Invertor - answer converts dc to ac Watts in one kilowatt hour - answer 3.6 mw Convert kelvin to celsius - answer subtract 273.15 from kelvin Positive temperature coefficient - answer the resistance of a metal increases when it's temperature is increased Aluminium or copper has lower resistivity? - answer copper Henry - answer unit of inductance Reactive power - answer also known as watt less power Brushes are made from - answer carbon Apparent power is measured in - answer va Improve power factor in ac circuit - answer fitting capacitor in parallel with load Hertz - answer cycles per second e.g. 30hz is 30 cycles a second Generator - answer coil of wire rotated in a magnetic field Xc - answer capacitive reactance Xl - answer inductive reactance
