Electronics Electrical Interview Questions, Tutorials, Circuits, Motors, Engines and more

the h-parameter or the hybrid parameters of a transistor helps us to analyse the amplifying action of transistor for small signal .

Why the antenna is called passive element?

Because It needs Some power input to broadcast or receive signals

what is the difference between inductance and resistance?
Inductance(L) is the property of a coil, which opposes change in current or In other words property of opposing AC.
Resistance(R) is the property of a matter or material which opposes the flow of electron.(it may be AC or DC)

Why 440volts instead of 660volts in 3 phases of supply system?

In single phase supply, 220V is voltage diff. between Line & neutral while, In 3 phase supply there are 3 supply lines phase shifted at 120deg from each other, so net voltage diff. (the phase resultant) between two phases in accordance with phase angle of 120deg is 440V.

However in 3 phase, 4 line systems having 1 neutral also, the voltage diff. between neutral and any of the phase is 220V..

this question is not any kind of technical question but if it has been asked in interview the

we can say that
1) ground wire
2) insulators

can be said as the circuit protection device

Which of the following are used to display measured quantity by digital meter?
LED,
LCD,
CRO?

differences between microprocessor and micro controller

In Microprocessor more op-codes, few bit handling instructions. But in Microcontroller: fewer op-codes, more bit handling Instructions, and also it is defined as a device that includes micro processor, memory, & input / output signal lines on a single chip.

The difference between microprocessor and microcontroller is the processor which can perform only software like operations it cannot control any parameters.hence the microcontroller will do that job.

In computers we are using the microprocessor and in industrial controls we are using microcontroller.

The microprocessor is the integration of a number of useful functions into a single IC package.

These functions are: The ability to execute a stored set of instructions to carry out user defined tasks. The ability to be able to access external memory chips to both read and write data from and to the memory.

Basically, a microcontroller is a device which integrates a number of the components of a microprocessor system onto a single microchip.
So a microcontroller combines onto the same microchip : The CPU core Memory (both ROM and RAM) Some parallel digital I/O Essentially, a microcontroller is obtained by integrating the key components of microprocessor,RAM, ROM, and Digital I/O onto the same chip die. Modern microcontrollers also contain a wealth of other modules such as Serial I/O, Timers, and Analogue to Digital Converters.

Design binary to gray code converter
It is easy to convert the binary number to gray number. First, for example take a binary number i.e ,101101.

Step 1: 101101 first write the MSB as it is i.e, darken bit i.e, 1

Step 2: add MSB and bit next to the MSB i.e, 1+0=1

Step 3: again add 0 and 1 we get i.e, 0+1=1
Step 4: again add 1 and 1 we get 1+1=0

Step 5: in previous step carry is occurred so neglect that carry . note that don't add carry to next add numbers
then again add 1+0 1+0=1

step 6: add 0+1 0+1= 1

Answer: Gray Code is : 111011

What are semiconductor devices

there are three types of materials. they are conductor , semi conductor and insulator.
where the semi conductor lies between the other two. ie. controlled conduction is possible in semi conductor.
thats why it is preferred in electronic devices.
A PN junction is formed in all the three types of materials. but in semi consuctor the junction is very thin and easy to break it with the very low voltage.

Which of the following is is used to hold ROM and RAM cards

1. Computer Bus 2. Expansion cards
3. Mother Board 4. Cache memory

The answer is mother board

what is meant by virtual ground in the op amp ?

The op amp connected in a negative feedback configuration, that is the o/p connected to the inverting terminal, tried to produce the same voltage at the inverting node as we applied to the non-inverting terminal, no matter whatever be the o/p. This happens because the opamp has a very high differential gain. so only way to not to clip or saturate the o/p in either positive or negative side is to make their both i/ps at the same potential. so when you apply the i/p to the inverting terminal and you connect the feedback to the inverting node, and your non-inverting terminal is grounded, then op amp tries to force the inverting node at the ground potential and whatever the difference between these two nodes are amplified.

How to convert binary to gray code and vice-versa?

How to measure the insulation resistance for printed circuit boards ?
By using known load impedance.

When transmitting digital signals is it necessary to transmit some harmonics in addition to fundamental frequency?
For asynchronous transmission, is it necessary to supply some synchronizing pulses additionally or to supply or to supply start and stop bit?
BPFSK is more efficient than BFSK in presence of noise. Why?
What is meant by pre-emphasis and de-emphasis?
Explain 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
Explain ASCII, EBCDIC?

What is the formula for power gain

power gain=output gain/input gain

What is D-FF?

What is the basic difference between Latches and Flip flops?

What is a multiplexer?

How can you convert an SR Flip-flop to a JK Flip-flop?

How can you convert an JK Flip-flop to a D Flip-flop?

What is Race-around problem? How can you rectify it?

Which semiconductor device is used as a voltage regulator and why?

Explain an ideal voltage source?

Explain zener breakdown and avalanche breakdown?

What are the different types of filters?

Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field. The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Even near absolute zero a real sample of copper shows a non-zero resistance. The resistance of a superconductor, on the other hand, drops abruptly to zero when the material is cooled below its "critical temperature". An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source.

Transponder: An automatic device that receives, amplifies, and retransmits a signal on a different frequency (see also broadcast translator).

Pull-up resistors are resistors used in the design of electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected. Pull-up resistors may also be used at the interface between two different types of logic devices, possibly operating at different power supply voltages.
The idea of a pullup resistor is that it weakly "pulls" the voltage of the wire it's connected to towards 5V (or whatever voltage represents a logic "high"). However, the resistor is intentionally weak (high-resistance) enough that, if something else strongly pulls the wire toward 0V, the wire will go to 0V.

BUS: In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus can logically connect several peripherals over the same set of wires. Each bus defines its set of connectors to physically plug devices, cards or cables together. Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus.

Difference between real ground and virtual ground
Virtual ground (sometimes called virtual earth) is an important concept found in electronic circuit designs. It identifies a point in a circuit as being held close to the circuit's ground or reference level electric potential. It is called virtual since this point does not have any real electrical connection to ground. The reference may or may not be the same as the local utility ground or earth
Real ground: Voltage is a differential quantity, which appears between two points. In order to deal only with a voltage (an electrical potential) of a single point, the second point has to be connected to a reference point (ground) having usually zero voltage. This point has to have steady potential, which does not vary when the electrical sources "attack" the ground by "injecting" or "sucking" a current to/from it. Usually, the power supply terminals serve as grounds; when the internal points of compound power sources are accessible, they can also serve as real grounds

Synchronous transmission uses no start and stop bits but instead synchronizes transmission speeds at both the receiving and sending end of the transmission using clock signals built into each component. A continual stream of data is then sent between the two nodes. Due to there being no start and stop bits the data transfer rate is quicker although more errors will occur, as the clocks will eventually get out of sync, and the receiving device would have the wrong time that had been agreed in protocol (computing) for sending/receiving data, so some bytes could become corrupted (by losing bits). Ways to get around this problem include re-synchronization of the clocks and use of check digits to ensure the byte is correctly interpreted and received.

Asynchronous transmission uses start and stop bits to signify the beginning bit ASCII character would actually be transmitted using 10 bits e.g.: A "0100 0001" would become "1 0100 0001 0". The extra one (or zero depending on parity bit) at the start and end of the transmission tells the receiver first that a character is coming and secondly that the character has ended. This method of transmission is used when data is sent intermittently as opposed to in a solid stream. In the previous example the start and stop bits are in bold. The start and stop bits must be of opposite polarity. This allows the receiver to recognize when the second packet of information is being sent.

Signal-to-noise ratio (often abbreviated SNR or S/N) defined as the ratio of a signal power to the noise power corrupting the signal. In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is.

What is meant by regenerative braking?

Answer:When the supply is cutt off for a running motor, it still continue running due to inertia. In order to stop it quickly we place a load(resitor) across the armature winding and the motor should have maintained continuous field supply. so that back e.m.f voltage is made to apply across the resistor and due to load the motor stops quickly.This type of breaking is called as "Regenerative Breaking".

What are the transformer losses?

Answer:TRANSFORMER LOSSES - Transformer losses have two sources-copper loss and magnetic loss. Copper losses are caused by the resistance of the wire (I2R). Magnetic losses are caused by eddy currents and hysteresis in the core. Copper loss is a constant after the coil has been wound and therefore a measurable loss. Hysteresis loss is constant for a particular voltage and current. Eddy-current loss, however, is different for each frequency passed through the transformer.

Define IDMT relay?

Answer:It is an inverse definite minimum time relay.In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates.It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.

Where should the lighting arrestor be placed in distribution lines?

Answer:Near distribution transformers and out going feeders of 11kv and incomming feeder of 33kv and near power transformers in sub-stations.

What is the difference between MCB & MCCB, Where it can be used?

Answer:MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition.under voltage and under frequency may be inbuilt. Normally it is used where normal current is more than 100A.

Why we do 2 types of earthing on transformer (ie:)body earthing & neutral earthing , what is function. i am going to install a 5oo kva transformer & 380 kva DG set what should the earthing value?

Answer:The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: body ( non conducting part)of the equipment shouldd be earthed to safegaurd the human beings.system Earthing : In this neutral of the supply source ( Transformer or Generator) should be grounded. With this,in case of unbalanced loading neutral will not be shifted.so that unbalanced voltages will not arise. We can protect the equipment also. With size of the equipment( transformer or alternator)and selection of relying system earthing will be further classified into directly earthed,Impedance earthing, resistive (NGRs) earthing.

Common-mode rejection ratio (CMRR) of a differential amplifier (or other device) measures the tendency of the device to reject input signals common to both input leads. A high CMRR is important in applications where the signal of interest is represented by a small voltage fluctuation superimposed on a (possibly large) voltage offset, or when relevant information is contained in the voltage difference between two signals.

What is the Polarization index value ? (pi value)and simple definition of polarization index ?

Answer:Its ratio between insulation resistance(IR)i.e meggar value

for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors & normally for motor to be in good condition it should be Greater than 2.5 .

what is the difference between synchronous generator & asynchronous generator?

Answer:In simple, synchronous generator supply's both active and reactive power but asynchronous generator(induction generator) supply's only active power and observe reactive power for magnetizing.This type of generators are used in windmills.

what is the principle of motor?

Answer:Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movement is called as torque.

Give two basic speed control scheme of DC shunt motor?

Answer:1. By using flux control method:in this method a rheostat is connected across the field winding to control the field current.so by changing the current the flux produced by the field winding can be changed, and since speed is inversely proportional to flux speed can be controlled 2.armature control method:in this method a rheostat is connected across armature winding by varying the resistance the value of resistive drop(IaRa)can be varied,and since speed is directly proportional to Eb-IaRa the speed can be controlled.

Which type of A.C motor is used in the fan (ceiling fan, exhaust fan, padestal fan, bracket fan etc) which are find in the houses ?

Answer:Its Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

What is the significance of vector grouping in Power Transformers?

Answer:Every power transformer has a vector group listed by its manufacturer. Fundamentally it tells you the information about how the windings are connected (delta or wye) and the phace difference betweent the current and voltage. EG. DYN11 means Delta primary, Wye Secondry and the current is at 11 o clock reffered to the voltage.

Advantages of vvvf drives over non vvvf drives for EOT cranes?

Answer:1.smooth start and stop.

2.no jerking of load.

3.exact posiitoning

4.better protection for motor.

5.high/low speed selection.

6.reliability of break shoe.

7.programmable break control.

8.easy circutry

9.reduction in controls

10.increases motor life

What is 2 phase motor?

Answer:A two phase motor is a motor with the the starting winding and the running winding have a phase split. e.g;ac servo motor.where the auxiliary winding and the control winding have a phase split of 90 degree.

whats the one main difference between UPS & inverter ? And electrical engineering & electronics engineering ?

Answer:uninterrupt power supply is mainly use for short time . means according to ups VA it gives backup. ups is also two types : on line and offline . online ups having high volt and amp for long time backup with with high dc voltage.but ups start with 12v dc with 7 amp. but inverter is startwith 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup.

What will happen when power factor is leading in distribution of power?

Answer:If their is high power factor, i.e if the power factor is close to one:

1.losses in form of heat will be reduced,

2.cable becomes less bulky and easy to carry, and very

cheap to afford, &

3. it also reduces over heating of tranformers.

What is vaccum currcuit breaker.define with cause and where be use it Device?

Answer:A breaker is normally used to break a ciruit. while breaking the circuit, the contact terminals will be separated. At the time of seperation an air gap is formed in between the terminals. Due to existing current flow the air in the gap is ionised and results in the arc. various mediums are used to quench this arc in respective CB's. but in VCB the medium is vaccum gas. since the air in the CB is having vaccum pressure the arc formation is interrupted. VCB's can be used upto 11kv.

what is ACSR cable and where we use it?

Answer:ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.

Which motor has high Starting Torque and Staring current DC motor, Induction motor or Synchronous motor?

Answer:DC Series motor has high starting torque. We can not start the Induction motor and Synchronous motors on load, but can not start the DC series motor without load.

what happen if we give 220 volts dc supply to d bulb r tube light?

Answer:Bulbs [devices] for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element.

what is meant by armature reaction?

Answer:The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

why, when birds sit on transmission lines or current wires doesn't get shock?
Answer:Its true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock.. so if a human touch single one line(phase) then he doesn't get shock if he is in the air (not touching - standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed - like neutral)। and in the most of electric lines the neutral is grounded..so that means that human who touch the line closes the circuit between phase and neutral.

what is the principle of motor?

Answer:Whenever a current carrying conductor is placed in an magnetic field it produce turning or twisting movemnt is called as torque.

Why Human body feel Electric shock ?? n in an Electric train during running , We did nt feel any Shock ? why?

Answer:Unfortunately our body is a pretty good conductor of electricity, The golden rule is Current takes the lowest resistant path if you have insulation to our feet as the circuit is not complete (wearing rubber footwear which doing some repairs is advisable as our footwear is a high resistance path not much current flows through our body).The electric train is well insulated from its electrical system.

What are the advantages of speed control using thyristor?

Answer:Advantages :1. Fast Switching Characterstics than Mosfet, BJT, IGBT 2. Low cost 3. Higher Accurate.

What is encoder, how it function?

Answer:An encoder is a device used to change a signal (such as a bitstream) or data into a code. The code may serve any of a number of purposes such as compressing information for transmission or storage, encrypting or adding redundancies to the input code, or translating from one code to another. This is usually done by means of a programmed algorithm,especially if any part is digital, while most analog encoding is done with analog circuitry.

whats is MARX CIRCUIT?

Answer:It is used with generators for charging a number of capacitor in parallel and discharging them in series.It is used when voltage required for testing is higher than the available.

How tube light circuit is connected and how it works?

Answer:A choke is connected in one end of the tube light and a starter is in series with the circuit. When supply is provided ,the starter will interrupt the supply cycle of AC. Due to the sudden change of supply the chock will generate around 1000volts . This volt will capable of to break the electrons inside the tube to make electron flow. once the current passes through the tube the starter circuit will be out of part. now there is no change of supply causes choke voltage normalized and act as minimize the current.

what is the diff. btwn. electronic regulator and ordinary rheostat regulator for fans?

Answer:The difference between the electronic and ordinary regulator is that in electronic reg. power losses are less because as we decrease the speed the electronic reg. give the power needed for that particular speed but in case of ordinary rheostat type reg. the power wastage is same for every speed and no power is saved.In electronic regulator triac is employed for speed control.by varying the firing angle speed is controlled but in rheostatic control resistance is decreased by steps to achieve speed control.

Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

Answer:Link is provided at a Neutral common point in the circuit from which various connection are taken for the individual control circuit and so it is given in a link form to withstand high Amps. But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only.So if any malfunction happen the fuse connected in the particular control circuit alone will blow off.

Operation carried out in Thermal power station?

Answer:The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to hit the turbine , the turbine which is coupled with the generator generates the electricity

What is "pu" in electrical engineering?

Answer:Pu stands for per unit and this will be used in power system single line diagram there it is like a huge electrical circuit with no of componenes (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of the component is considered as base values, then all other component ratings will get back into this basis.Those values are called as pu values. (p.u=actual value/base value).

How can you start-up the 40w tube lite with 230v AC/DC without using any choke/Coil?

Answer:It's possible by means of Electronic choke.otherwise it's not possible to ionize the particles in tube. light, with normal voltage.

What is electric traction?

Answer:Traction means using the electric power for traction system i.e. for railways,trams, trolleys etc. electric traction means use of the electricity for all these . now a days, magnetic traction is also used for bullet trains. basically dc motors are used for electric traction systems.

Infinite impulse response (IIR) is a property of signal processing systems. They have an impulse response function which is non-zero over an infinite length of time. The simplest analog IIR filter is an RC filter made up of a single resistor (R) feeding into a node shared with a single capacitor (C). This filter has an exponential impulse response characterized by an RC time constant.

Impulse response of a system is its output when presented with a very brief input signal, an impulse. A system in the class known as LTI systems (linear, time-invariant systems) is completely characterized by its impulse response. The Laplace transform of the impulse response function is known as the transfer function. It is usually easier to analyze systems using transfer functions as opposed to impulse response functions. The Laplace transform of a system's output may be determined by the multiplication of the transfer function with the input function in the complex plane, also known as the frequency domain. An inverse Laplace transform of this result will yield the output function in the time domain. To determine an output function directly in the time domain requires the convolution of the input function with the impulse response function.

Finite impulse response (FIR) filter is a type of a digital filter. The impulse response, the filter's response to a Kronecker delta input, is 'finite' because it settles to zero in a finite number of sample intervals. This is in contrast to infinite impulse response filters which have internal feedback and may continue to respond indefinitely.
A FIR filter has a number of useful properties which sometimes make it preferable to an infinite impulse response filter. FIR filters:
* Are inherently stable. This is due to the fact that all the poles are located at the origin and thus are located within the unit circle.
* Require no feedback. This means that any rounding errors are not compounded by summed iterations. The same relative error occurs in each calculation.
* They can be designed to be linear phase, which means the phase change is proportional to the frequency.

Ideal voltage source is a circuit element where the voltage across it is independent of the current through it. It only exists in mathematical models of circuits. If the voltage across an ideal voltage source can be specified independently of any other variable in a circuit, it is called an independent voltage source.

Relationship

All materials are made up from atoms, and all atoms consist of protons, neutrons and electrons. Protons, have a positive electrical charge. Neutrons have no electrical charge while Electrons, have a negative electrical charge. Atoms are bound together by powerful forces of attraction existing between the atoms nucleus and the electrons in its outer shell. When these protons, neutrons and electrons are together within the atom they are happy and stable. However, if we separate them they exert a potential of attraction called a potential difference. If we create a circuit or conductor for the electrons to drift back to the protons the flow of electrons is called a current. The electrons do not flow freely through the circuit, the restriction to this flow is called resistance. Then all basic electrical or electronic circuit consists of three separate but very much related quantities, Voltage, ( v ), Current, ( i ) and Resistance, ( Ω ).

Voltage

Voltage is the potential energy of an electrical supply stored in the form of an electrical charge. Voltage can be thought of as the force that pushes electrons through a conductor and the greater the voltage the greater is its ability to "push" the electrons through a given circuit. As energy has the ability to do work this potential energy can be described as the work required in joules to move electrons in the form of an electrical current around a circuit from one point or node to another. The difference in voltage between any two nodes in a circuit is known as the Potential Difference, p.d. sometimes called Voltage Drop.

The Potential difference between two points is measured in Volts with the circuit symbol V, or lowercase "v", although Energy, E lowercase "e" is sometimes used. Then the greater the voltage, the greater is the pressure (or pushing force) and the greater is the capacity to do work.

A constant voltage source is called a DC Voltage with a voltage that varies periodically with time is called an AC voltage. Voltage is measured in volts, with one volt being defined as the electrical pressure required to force an electrical current of one ampere through a resistance of one Ohm. Voltages are generally expressed in Volts with prefixes used to denote sub-multiples of the voltage such as microvolts ( μV = 10^-6 V ), millivolts ( mV = 10^-3 V ) or kilovolts ( kV = 10³ V ). Voltage can be either positive or negative.

Batteries or power supplies are mostly used to produce a steady D.C. (direct current) voltage source such as 5v, 12v, 24v etc in electronic circuits and systems. While A.C. (alternating current) voltage sources are available for domestic house and industrial power and lighting as well as power transmission. The mains voltage supply in the United Kingdom is currently 230 volts a.c. and 110 volts a.c. in the USA. General electronic circuits operate on low voltage DC battery supplies of between 1.5V and 24V d.c. The circuit symbol for a constant voltage source usually given as a battery symbol with a positive, + and negative, - sign indicating the direction of the polarity. The circuit symbol for an alternating voltage source is a circle with a sine wave inside.

Voltage Symbols

A simple relationship can be made between a tank of water and a voltage supply. The higher the water tank above the outlet the greater the pressure of the water as more energy is released, the higher the voltage the greater the potential energy as more electrons are released. Voltage is always measured as the difference between any two points in a circuit and the voltage between these two points is generally referred to as the "Voltage drop". Any voltage source whether DC or AC likes an open or semi-open circuit condition but hates any short circuit condition as this can destroy it.

Electrical Current

Electrical Current is the movement or flow of electrical charge and is measured in Amperes, symbol i, for intensity). It is the continuous and uniform flow (called a drift) of electrons (the negative particles of an atom) around a circuit that are being "pushed" by the voltage source. In reality, electrons flow from the negative (-ve) terminal to the positive (+ve) terminal of the supply and for ease of circuit understanding conventional current flow assumes that the current flows from the positive to the negative terminal. Generally in circuit diagrams the flow of current through the circuit usually has an arrow associated with the symbol, I, or lowercase i to indicate the actual direction of the current flow. However, this arrow usually indicates the direction of conventional current flow and not necessarily the direction of the actual flow.

Conventional Current Flow

Conventionally this is the flow of positive charge around a circuit. The diagram at the left shows the movement of the positive charge (holes) which flows from the positive terminal of the battery, through the circuit and returns to the negative terminal of the battery. This was the convention chosen during the discovery of electricity in which the direction of electric current was thought to flow in a circuit. In circuit diagrams, the arrows shown on symbols for components such as diodes and transistors point in the direction of conventional current flow. Conventional Current Flow is the opposite in direction to the flow of electrons.

Electron Flow

The flow of electrons around the circuit is opposite to the direction of the conventional current flow. Electron Flow The current flowing in a circuit is composed of electrons that flow from the negative pole of the battery (the cathode) and return to the positive pole (the anode). This is because the charge on an electron is negative by definition and so is attracted to the positive terminal. The flow of electrons is called Electron Current Flow. Therefore, electrons flow from the negative terminal to the positive.

Both conventional current flow and electron flow are used by many textbooks. In fact, it makes no difference which way the current is flowing around the circuit as long as the direction is used consistently. The direction of current flow does not affect what the current does within the circuit. Generally it is much easier to understand the conventional current flow - positive to negative.

In electronic circuits, a current source is a circuit element that provides a specified amount of current for example, 1A, 5A 10 Amps etc, with the circuit symbol for a constant current source given as a circle with an arrow inside indicating its direction. Current is measured in Amps and an amp or ampere is defined as the number of electrons or charge (Q in Coulombs) passing a certain point in the circuit in one second, (t in Seconds). Current is generally expressed in Amps with prefixes used to denote micro amps (μA = 10^-6A) or milli amps (mA = 10^-3A). Electrical current can be either positive or negative.

Current that flows in a single direction is called Direct Current, or D.C. and current that alternates back and forth through the circuit is known as Alternating Current, or A.C.. Whether AC or DC current only flows through a circuit when a voltage source is connected to it with its "flow" being limited to both the resistance of the circuit and the voltage source pushing it. Also, as AC currents (and voltages) are periodic and vary with time the "effective" or "RMS", (Root Mean Squared) value given as I_rms produces the same average power loss equivalent to a DC current I_average . Current sources are the opposite to voltage sources in that they like short or closed circuit conditions but hate open circuit conditions as no current will flow.

Using the tank of water relationship, current is the equivalent of the flow of water through the pipe with the flow being the same throughout the pipe. The faster the flow of water the greater the current. Any current source whether DC or AC likes a short or semi-short circuit condition but hates any open circuit condition as this prevents it from flowing.

Resistance

The Resistance of a circuit is its ability to resist or prevent the flow of current (electron flow) through it making it necessary to apply a bigger voltage to the circuit to cause the current to flow again. Resistance is measured in Ohms, Greek symbol ( Ω, Omega ) with prefixes used to denote Kilo-ohms (kΩ = 10³Ω) and Mega-ohms (MΩ = 10⁶Ω). Resistance cannot be negative only positive.

Resistor Symbols

The amount of resistance determines whether the circuit is a "good conductor" - low resistance, or a "bad conductor" - high resistance. Low resistance, for example 1Ω or less implies that the circuit is a good conductor made from materials such as copper, aluminium or carbon while a high resistance, 1MΩ or more implies the circuit is a bad conductor made from insulating materials such as glass, porcelain or plastic. A "semiconductor" on the other hand such as silicon or germanium, is a material whose resistance is half way between that of a good conductor and a good insulator. Semiconductors are used to make Diodes and Transistors etc.

Resistance can be linear in nature or non-linear in nature. Linear resistance obeys Ohm's Law and controls or limits the amount of current flowing within a circuit in proportion to the voltage supply connected to it and therefore the transfer of power to the load. Non-linear resistance, does not obey Ohm's Law but has a voltage drop across it that is proportional to some power of the current. Resistance is pure and is not affected by frequency with the AC impedance of a resistance being equal to its DC resistance and as a result can not be negative. resistance is always positive. Also, resistance is an attenuator which has the ability to change the characteristics of a circuit by the effect of load resistance or by temperature which changes its resistivity.

For very low values of resistance, for example milli-ohms, (mΩ´s) it is sometimes more easier to use the reciprocal of resistance (1/R) rather than resistance (R) itself. The reciprocal of resistance is called Conductance, symbol (G) and it is the ability of a conductor or device to conduct electricity with high values of conductance implying a good conductor and low values of conductance implying a bad conductor. The unit of conductance is the Siemen, symbol (S).

Again, using the water relationship, resistance is the diameter or the length of the pipe the water flows through. The smaller the diameter of the pipe the larger the resistance to the flow of water, and therefore the larger the resistance.

Relationship between Voltage and Current in a circuit of constant resistance.

Summary

Hopefully by know you have an idea of how voltage, current and resistance are related. The relationship between Voltage, Current and Resistance forms the basis of Ohm's law which in a linear circuit states that if we increase the voltage, the current goes up and if we increase the resistance, the current goes down. A basic summary of the three units is given below.

Voltage or potential difference is the measure of potential energy between two points in a circuit and is commonly referred to as its "volt drop".
When a voltage source is connected to a closed loop circuit the voltage will produce a current flowing around the circuit.
In D.C. voltage sources the symbols +ve (positive) and -ve (negative) are used to denote the polarity of the voltage supply.
Voltage is measured in "Volts" and has the symbol "V" for voltage or "E" for energy.
Current flow is a combination of electron flow and hole flow through a circuit.
Current is the continuous and uniform flow of charge around the circuit and is measured in "Amperes" or "Amps" and has the symbol "I".
The effective (rms) value of an AC current has the same average power loss equivalent to a DC current flowing through a resistive element.
Resistance is the opposition to current flowing around a circuit.
Low values of resistance implies a conductor and high values of resistance implies an insulator.
Resistance is measured in "Ohms" and has the Greek symbol "Ω" or the letter "R".

Quantity	Symbol	Unit of Measure	Abbreviation
Voltage	V or E	Volt	V
Current	I	Amp	A
Resistance	R	Ohms	Ω

In the next tutorial about DC Theory we will look at Ohms Law which is a mathematical equation explaining the relationship between Voltage, Current, and Resistance within electrical circuits and is the foundation of electronics and electrical engineering. Ohm's Law is defined as: E = I x R

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Relationship

Voltage

Voltage Symbols

Electrical Current

Conventional Current Flow

Electron Flow

Resistance

Resistor Symbols

Summary

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