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 Question: What is Thevenin's theorem ? Answer: Thevenin's Theorem The Thevenin's theorem states that any linear network can be represented by a voltage source in series with an impedance. We will generally use a simpler version: any circuit made up of voltage sources, current sources and resistors can be replaced by a voltage and a resistor. When applying the Thevenin Theorem there are three cases. Case 1: Only independent sources . In the typical case, there are no dependent sources in the circuit to be Thevenized. To find the Thevenin equivalent, first find the open circuit voltage, Voc, this is the Thevenin voltage. To find the Thevenin resistance, set all sources to zero and find the resistance of the resulting circuit Consider again the circuit from above, and try to find the Thevenin circuit at the terminals (i.e., across the 1k resistor). From the discussion of superposition, we know the open circuit voltage, Voc, is 1.666 volts. The Thevenin resistance, RT, is found by finding the equivalent resistance of the circuit with all source set to zero, as shown below   Obviously the Thevenin resistance, RT, is 1k||500=333W. Therefore the resulting circuit is: Case 2: Independent and Dependent Sources. If the circuit to be Thevenized has both dependent and independent source, the method described above cannot be used to find the Thevenin resistance. Instead, you must find the short circuit current, Isc (current through short circuit at terminals). Then the Thevenin resistance is given by RT=Voc/Isc.

 Question: What are the main concepts of Superposition Theorem? Answer: The superposition theorem is a method of solving circuits, often used in circuits with more than one emf source. In a network containing multiple independent source, each source can be applied independently with the reaming source turned off. In order to use one source at a time, all other sources are "killed" temporarily.This means disabling the source so that it can not generate voltage or current, with out changing the resistance of the circuit.Keep these point in mind .(i) A voltage source such as a battery is killed or turned off by assuming a short circuit across its potential difference.(ii) A current source is killed or turned off by replacing it with an open circuit.(iii) The result obtained by applying each source independently are then added together algebraically to obtain a solution.

 Question: What is Norton's Theorem ? Answer: • Norton's Theorem is a way to reduce a network to an equivalent circuit composed of a single current source, parallel resistance, and parallel load. • Steps to follow for Norton's Theorem: • (1) Find the Norton source current by removing the load resistor from the original circuit and calculating current through a short (wire) jumping across the open connection points where the load resistor used to be. • (2) Find the Norton resistance by removing all power sources in the original circuit (voltage sources shorted and current sources open) and calculating total resistance between the open connection points. • (3) Draw the Norton equivalent circuit, with the Norton current source in parallel with the Norton resistance. The load resistor re-attaches between the two open points of the equivalent circuit. • (4) Analyze voltage and current for the load resistor following the rules for parallel circuits.

 Question: What is peak voltage? Answer: Peak voltage tell you how far the voltage swings, either positive or negative, from the point of reference. Peak voltage is only a moderately useful way of measuring voltage when trying to express the amount of work that will be done when driving a specified load. Some manufacturers use peak voltage to get the power output ratings of their amplifiers. For Figure Click Here

 Question: What is RMS voltage ? Answer: RMS voltage is absolutely the most common way to measure/quantify AC voltage. It is also the most useful. Because AC voltage is constantly changing and is at or near the highest and lowest points in the cycle for only a tiny fraction of the cycle, the peak voltage is not a good way to determine how much work can be done by an AC power source (e.g. your amplifier, a wall outlet in your house...). DC voltage is constant. Its voltage level can be plugged directly into the formulas for power and you will get an accurate image of its ability to do work. RMS voltage will give you the same ability to predict how much work will be done by an AC voltage. The RMS voltage of a Pure sine wave is approximately .707*peak voltage. If you read voltage with a voltmeter you are generally given the RMS voltage of the wave form. Some meters display an 'average' voltage which is very close to RMS. When reading voltage with a voltmeter, the display indicates the RMS or average voltage not the peak or peak-peak voltage. *If the waveform isn't a pure sine wave (like a square wave or a signal with mixed sine waves of different frequencies or music), multiplying the peak times .707 will not give an accurate RMS value and therefore will not give an accurate indication of the work that the waveform can produce when driving a load. For more complex signals, you need a meter that will calculate the RMS value from a set of samples taken at regular intervals. For Figure Click Here

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 Question: What is an Ideal diode? Answer: The diode can be considered to be a one way street, that is it conducts electricity well in one direction but hardly any in the opposite direction. An ideal diode has no resistance in the forward direction and infinite resistance in the reverse direction. An ideal diode is like a light switch in your home. When the switch is closed, the circuit is completed; and the light turns on. When the switch is open, there is no current and the light is off.However, the diode has an additional property; it is unidirectional, i.e. current flows in only one direction (anode to cathode internally).When a forward voltage is applied, the diode conducts; and when a reverse voltage is applied, there is no conduction. A mechanical analogy is a rat chat, which allows motion in one direction only.

 Question: What is source transformation? Answer: Source Transformation method is used to find unknown value of a voltage or current in a circuit.If we have any source embedded within a network, say this source is a current source having a value I & there exists a resistance having a value R, in parallel to it. We can replace it with a voltage source of value V=IR in series with same resistance R.The reverse is also true that is a voltage source V, in series with a resistance R can be replaced by a current source having a value I=V/RIn parallel to the resistance R.Parameters within circuit, for example an output voltage remain unchanged under these transformations.

 Question: What is a function of diode? Answer: Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves. To see the figure please click here. A diode is made of two different types of semiconductors right next to each other. One side is easy for electrons to travel through; one side is much tougher. It's something like trying to swim through a pool filled with water and then a pool filled with mud: swimming through water is easy; swimming through mud is next to impossible. To an electron some semiconductors seem like water, some like mud.One side of the semiconductor boundary is like mud, one like water. If you try to get electricity to move from the mud side to the water side, there's no problem. The electrons just jump across the boundary, forming a current. But try to make electricity go the other way and nothing will happen. Electrons that didn't have to work hard to travel around the water side just don't have enough energy to make it into the mud side. (In real life, there are always a few electrons that can trickle in the wrong direction, but not enough to make a big difference.There are a number of different electronic devices which tend to be called diodes. Although they're made differently they all have three things in common. 1. They have two leads like a resistor. 2. The current they pass depends upon the voltage between the leads. 3. They do not obey Ohm's law! As an example we will use a typical diode called a pn-junction. This allows us to explain behavior of diodes. Remember, however, that there are other sorts of diodes which are built differently but show the same general behavior. We create a pn-junction by joining together two pieces of semiconductor, one doped n-type, the other p-type. This causes a depletion zone to form around the junction (the join) between the two materials. This zone controls the behavior of the diode.

 Question: What is meant by Forward Voltage Drop ? Answer: Electricity uses up a little energy pushing its way through the diode, rather like a person pushing through a door with a spring. This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon.

 Question: What is meant by "Reverse Voltage" in a diode? Answer: Reverse Voltage When a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a very tiny current of a few µA or less. This can be ignored in most circuits because it will be very much smaller than the current flowing in the forward direction. However, all diodes have a maximum reverse voltage (usually 50V or more) and if this is exceeded the diode will fail and pass a large current in the reverse direction, this is called breakdown.

 Question: What is passive sign Connvention? Answer: The passive sign convention: When we observe that positive current enters the positive terminal of a component, we say that the component obeys the passive sign convention (PSC). Therefore, when the passive sign convention is being obeyed, it indicates that a component is dissipating energy (or power) as charge is being displaced from a higher potential to a lower potential. One way to think about this is using another water analogy. If we splice a garden hose in a length of fire hose we create a pressure potential. The high pressure side is the one where the water is entering. The garden hose is analogous to a resistor which impedes the flow of current. Thus, when current flows through a resistor, a higher voltage potential will exist on the incoming current side. In this example, the garden hose and the resistor are obeying the passive sign convention. To reiterate, the PSC is obeyed when the current enters an element’s positive terminal and exits at the negative terminal. The passive sign convention is usually used for assigning reference marks for voltage drops across, and currents through, resistors, but we frequently assign a current and associated direction for a current through a voltage source in violation of the PSC. By the same token, we frequently define a voltage and its associated reference marks across a current source in violation of the PSC. To successfully apply Ohms law, you must consistently observe the proper relationship between applied voltage and the direction of current flow. See this image

 Question: What is resistance? Answer: Resistance Resistance is a term that describes the forces that oppose the flow of electron current in a conductor. All materials naturally contain some resistance to the flow of electron current. We have not found a way to make conductors that do not have some resistance. If we use our water analogy to help picture resistance, think of a hose that is partially plugged with sand. The sand will slow the flow of water in the hose. We can say that the plugged hose has more resistance to water flow than does an unplugged hose. If we want to get more water out of the hose, we would need to turn up the water pressure at the hydrant. The same is true with electricity. Materials with low resistance let electricity flow easily. Materials with higher resistance require more voltage (EMF) to make the electricity flow. The scientific definition of one ohm is the amount of electrical resistance that exists in an electrical circuit when one amp of current is flowing with one volt being applied to the circuit. Resistance depends upon the following factors a) length b) area            c) temperature                             R= r *L/A     Is resistance good or bad? Resistance can be both good and bad. If we are trying to transmit electricity from one place to another through a conductor, resistance is undesirable in the conductor. Resistance causes some of the electrical energy to turn into heat so some electrical energy is lost along the way. However, it is resistance that allows us to use electricity for heat and light. The heat that is generated from electric heaters or the light that we get from light bulbs is due to resistance. In a light bulb, the electricity flowing through the filament, or the tiny wires inside the bulb, cause them to glow white hot. If all the oxygen were not removed from inside the bulb, the wires would burn up. An important point to mention here is that the resistance is higher in smaller wires. Therefore, if the voltage or EMF is high, too much current will follow through small wires and make them hot. In some cases hot enough to cause a fire or even explode. Therefore, it is sometimes useful to add components called resistors into an electrical circuit to slow the flow of electricity and protect of the components in the circuit. Resistance is also good because it gives us a way to shield ourselves from the harmful energy of electricity.

 Question: What is indcctance? Answer: INDUCTANCE:The characteristic of an electrical circuit that opposes a change in current. The reaction (opposition) is caused by the creation or destruction of a magnetic field. When current starts to flow, magnetic lines of force are created. These lines of force cut the conductor inducing a counter emf in a direction that opposes current.

Question: What is Power dissipation?

# Power dissipation

When a current flows through a component, that component will heat up. This process is called power dissipation and is measured in Watts. The power dissipation of a device can be calculated very easily:
P = V · I
Let's calculate the power dissipation of a 100 ohms resistor connected to a 9V battery.
The voltage across the resistor will be 9V. The current is 9V/100ohms = 90mA. So the power dissipation will be: 9V · 90mA = 810mW.
It is very important to calculate the power dissipation of the components in your design. A regular resistor has a maximum dissipation rating of 0.25W (= 250mW). If you would have used such a resistor in the example above, it would have blown. A 1W resistor is a good choice.
Since it's so important, let's create an equation with which we can easily calculate the power dissipation of a resistor. We know:
P = V · I ----(1)

V = I · R ----(2)

I = V / R ----(3)
Substituting (2) in (1) and (3) in (1) respectively results in:
P = I2 · R

P = V2 / R
With these equations you can easily calculate the power dissipation when you connect a DC voltage source to a resistor.

 Question: What is an open circuit? Answer: An open circuit: A circuit element with resistance approaching infinity. (R=¥). See this figure..

 Question: What is meant by " Branch " ? Answer: Branches A branch is any path in the circuit that has a node at each end and contains at least one voltage source or resistor but contains no other nodes. This circuit contains 6 branches, denoted B1, ..., B6.If branch B4 did not contain a resistor then it could be deleted and nodes N2 and N3 could be considered one and the same node. See this figure.

 Question: What are the rules for parallel and series resistances in a network or circuit? Answer: Keep these two things in mind when you are solving such circuits.Resistors are in series if they carry exactly the same current (share one common node).Resistors are in parallel if they have the same voltage across them and are connected exactly between the same two nodes.

 Question: What is ground? Answer: GroundEvery electrical circuit has a point of reference to which all circuit voltages are compared. This reference point is called ground, and circuit voltages are either positive or negative with respect to ground. Connections to ground that are made for safety reasons refer to earth ground. When voltage measurements are taken, the difference of potential between a point in the circuit and a ground point is measured by the voltmeter. This type of ground is referred to as chassis or common ground.Earth Ground.Initially, ground referred to the earth itself and since has represented a point of zero potential or zero volts. A short circuit within a device that connects live voltage to the frame could cause a serious shock to anyone touching it. However, if the frame is connected to earth ground, it is held at the safe potential of zero volts, as the earth itself absorbs the voltage.

 Question: What is the difference b/w independent and dependent sources? Answer: Independent Voltage SourceAn independent voltage source is a two terminal element that maintain a specified voltage between its terminals regardless of the current through it.The general symbol for an independent source is ciricle. Dependent Voltage SourceDependent or controlled voltage source generate a voltage that is determined by a voltage at a specified location in the circuit.Such sources are very important bcause they are integral part of our mathmatical models.The general symbol for dependent voltage source is diamond

 Question: What is meant by "Super Node" ? Answer: A node which emerges as a result of combination of two ordinary nodes around a voltage source is called a super node.

 Question: How can we write Constraint or Coupling equation for super node? Answer: Constraint or coupling equation describes a super node mathematically, instead of writing equations individual ordinary nodes of the super node.The difference in potential between the two nodes is equal to voltage source between two nodes.Now to write constraint equation first write the node which is towards +ve terminal of voltage source then subtract the node which is towards -ve side of voltage source then equal this difference to value of voltage source.

Question: What is the differnce between series and parallel networks or circuits?

### Series circuits

A series circuit is a circuit in which resistors are arranged in a chain, so the current has only one path to take. The current is the same through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors:

equivalent resistance of resistors in series : R = R1 + R2 + R3 + ... A series circuit is shown in the diagram above. The current flows through each resistor in turn. If the values of the three resistors are:

R1= 8ohm, R2= 8ohm, and R3=4ohm, the total resistance is 8+8+4=20ohm

With a 10 V battery, by V = I R the total current in the circuit is:

I = V / R = 10 / 20 = 0.5 A. The current through each resistor would be 0.5 A.

### Parallel circuits

A parallel circuit is a circuit in which the resistors are arranged with their heads connected together, and their tails connected together. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The voltage across each resistor in parallel is the same.

The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total:

equivalent resistance of resistors in parallel: 1 / R = 1 / R1 + 1 / R2 + 1 / R3 +... A parallel circuit is shown in the diagram above. In this case the current supplied by the battery splits up, and the amount going through each resistor depends on the resistance. If the values of the three resistors are:

R1= 8ohm, R2=8om, and R3=4ohm, the total resistance is found by

1/R=1/8 + 1/8 + 1/4 =1/2. This gives R=2ohm

With a 10 V battery, by V = I R the total current in the circuit is: I = V / R = 10 / 2 = 5 A.

The individual currents can also be found using I = V / R. The voltage across each resistor is 10 V, so:

I1 = 10 / 8 = 1.25 A
I2 = 10 / 8 = 1.25 A
I3=10 / 4 = 2.5 A

Note that the currents add together to 5A, the total current.

### Circuits with series and parallel components

Many circuits have a combination of series and parallel resistors. Generally, the total resistance in a circuit like this is found by reducing the different series and parallel combinations step-by-step to end up with a single equivalent resistance for the circuit. This allows the current to be determined easily. The current flowing through each resistor can then be found by undoing the reduction process.

General rules for doing the reduction process include:

1. Two (or more) resistors with their heads directly connected together and their tails directly connected together are in parallel, and they can be reduced to one resistor using the equivalent resistance equation for resistors in parallel.

2. Two resistors connected together so that the tail of one is connected to the head of the next, with no other path for the current to take along the line connecting them, are in series and can be reduced to one equivalent resistor.

Finally, remember that for resistors in series, the current is the same for each resistor, and for resistors in parallel, the voltage is the same for each one.

 Question: What is kirchhoff's current Law (KCL)and Voltage Law (KVL)? Answer: Kirchhoff's Current Law This fundamental law results from the conservation of charge. It applies to a junction or node in a circuit -- a point in the circuit where charge has several possible paths to travel. In Figure 1, we see that IA is the only current flowing into the node. However, there are three paths for current to leave the node, and these current are represented by IB, IC, and ID. Once charge has entered into the node, it has no place to go except to leave (this is known as conservation of charge). The total charge flowing into a node must be the same as the the total charge flowing out of the node. So, IB + IC + ID = IA Bringing everything to the left side of the above equation, we get (IB + IC + ID) - IA = 0 Then, the sum of all the currents is zero. This can be generalized as follows  SI = 0 Note the convention we have chosen in Fig 1: current flowing into the node are taken to be negative, and currents flowing out of the node are positive. It should not really matter which you choose to be the positive or negative current, as long as you stay consistent. However, it may be a good idea to find out the convention used in your class. Kirchhoff's Voltage Law Kirchhoff's Voltage Law (or Kirchhoff's Loop Rule) is a result of the electrostatic field being conservative. It states that the total voltage around a closed loop must be zero. If this were not the case, then when we travel around a closed loop, the voltages would be indefinite. So SV = 0 In Fig 2 the total voltage around loop 1 should sum to zero, as does the total voltage in loop2. Furthermore, the loop which consists of the outer part of the circuit (the path ABCD) should also sum to zero.

 Question: What is meant by "Loop" ? Answer: A loop is a closed path formed by starting at a node, passing through a set of nodes, and returning to the starting node without passing through any node more than once.

 Question: What is meant by "Junction" ? Answer: junction and node both are the same things,node is also called junction.It is the contact point between two or more than two elements or we can say that it is the point of connection between circuit.See this figure. This figure will help you to understand

 Question: What is reference node? Answer: The reference node is commonly called the ground since it is assumed to have zero potential. The choice of a reference node is completely arbitrary, but the node with the largest number of components or voltage source connected to it is usually most convenient.Generally when we are choosing refrence node on paper we will consider the bottom node of the circuit as refrence node. See this figure

 Question: Define Shells and sub Shells Answer: Schematically energy levels of electrons in an atom are represented by shells and sub shells. Since in a sense electrons are moving around the nucleus, they possess orbital angular moment. Now different orientations of angular moment, having same magnitude, contribute to the same energy or energy level, we call that energy level as orbit or shell, and different orientations of orbital angular moment which contribute to the same shell, as orbitals or sub shells. Shells are denoted as K, L, M,…., and sub shells are denoted as s,p,d,…. and so on. Technically shells are represented by ‘n’ which can have values 1,2,3,…. (corresponds to K,L,M,… respectively) and sub shells as ‘l’ having values0, +1,+2,......(n-1) , corresponding to s,p,d,…. respectively. Beside orbital momentum, electrons also carry spin momentum due to their motion around their own axis. Electron carry either +1/2 or -1/2 spins. Quantum theory also give a simple formula for maximum occupancy of each shell, and it is , ‘n’ is the number of any shell. So K (n=1) can accommodate only 2 electrons, L 8, M 18, and so on. This figure schematically shows shells and sub shells of an atom. Check out this java applet to see different real images of shells and sub shells of hydrogen atom.

 Question: What is Conductor? Answer: Conductors are material from which electric current can pass easily. Conductors have negligible resistance for the passage of current. Every material in the world can be defined in terms of how well it conducts electricity. Certain things, such as cold glass, never conduct electricity. They're known as insulators. Materials which do conduct electricity, like copper, are called conductors. In the middle are materials known as semiconductors, which don't conduct as well as conductors, but can carry current. Last, are materials called superconductors, which when brought down to very low temperatures turn into superhighways of current -- they conduct electricity without any resistance whatsoever. All these different materials are made of atoms that look basically alike: a nucleus with electrons circling around them. What makes them so different when it comes to conducting electricity? The difference comes down to nothing more than how the electrons are arranged around the nucleus. The laws of quantum physics say that there are only specific bands (or tracks) in which any electron can travel. There are some interesting facts about these bands. First of all, only a very specific number of electrons can travel in each one; once it's full, it's full. Second, which track an electron is in corresponds to how much energy that electron has. And third, some of the bands are closer to each other than others. Different atoms have different numbers of electrons, and how those electrons are arranged in the bands defines whether a material made of those atoms will conduct. In every atom, the electrons crowd down as close to the nucleus as possible, since the bands that are closest to the nucleus are also the ones that require the least energy. That means that the outermost track might not be completely filled. If it's not filled, then it's easy for an electron to jump from one atom into an empty space in the atom next door. Moving electrons, and therefore an electrical current. Atoms with empty spaces in the outermost electron bands are conductors. Let's go to the next scenario, where the outermost track is completely filled. If the electrons in this track were given a little kick of energy -- say from a flash of light -- they might have enough energy to jump up to to the next, empty track. But remember, some bands are close to each other, and some aren't. In atoms where the next track is close by, an energetic electron will have no problem jumping up a track. Suddenly, this electron is in a track with empty spaces, and electrons can move from atom to atom just as described above. Since these kinds of atoms can only conduct electricity sometimes -- when given this outside jolt of energy -- they're the semiconductors. Atoms with a full outside track which is very close to the next empty track are semiconductors. If, however, the next potential track is too far away, then an electron can't jump to it even if it's given a jolt of energy. These electrons will always stick in their assigned track, never allowed to roam to another atom -- and never forming current. Atoms with a full outside track which is far from the next empty track are insulators. Superconductors are a whole different breed, since no material known today super conducts except at very cold temperatures. Scientists are discovering materials that do super conduct closer and closer to room temperature all the time, but no one is quite sure how that happens. However, John Bardeen, Leon Cooper, and Robert Schrieffer did come up with a theory for how the very coldest superconductors work, known as the BCS theory. In such materials, at low temperatures, the atoms vibrate in a way that forces the moving electrons closer together. Normally electrons don't like to huddle so close, since they're all electrically negative and therefore repel each other. But in superconductors, the electrons actually achieve almost an attraction for each other. The result is that as one electron moves, it pulls the next electron along right behind it. Electrons slip from atom to atom more easily than they ever do normally. Atoms which, at the right temperature, can make electrons attract instead of repel each other are superconductors.

 Question: What is Polarity? Answer: The negative polarity has been assigned to the static charge produced on rubber, amber and resinous materials in general. Positive polarity refers to the static charge produced on glass and other vitreous materials. On this basis the electrons in all atoms are basic particles of negative charge because their polarity is the same as the charge on rubber. Protons have positive charge because the polarity is the same as the charge on glass.

 Question: What is Conventional Current? Why always electron flow from Negitive to Positive ? Can it flow in reverse direction? Answer: The motion of positive charge, in the opposite direction from electron flow, is considered as conventional current.Electricity was known of long before Benjamin Franklin. It was not understood very well, but it was known of. Scientists knew there were two kinds of electric charge. They knew there was electric current. Scientists believed that the opposite charges moved similarly in opposite directions. They defined one as positive and one as negative. They defined current to be in the direction of the positive charges. Later, they learned of their mistake.Only the negative charges move freely in conductors. Electrons had been defined as the negative charges. Current had been defined "backwards". It was too late to redefine all of electrical physics, so the inconvenience holds to this day. The direction that the electrons move is opposite the direction that current points. Because of how electricity works, it isn't much of a problem. Negative charge moving to the left through a wire has the same effect as positive charge moving to the right. So long as the total charge in the wire (protons and electrons) remains balanced, no trouble occurs.See this interesting link

 Question: What is a short circuit? Answer: A circuit element with resistance approaching zero. (R = 0)See this figure.In short circuit voltage source has a closed path across its terminals.in other words connecting both the terminals of voltage source without the resistance between them.the result is too much current in the circuit.For instance ,a short across the conducting wires for a bulb produces too much current in the wires but no current through the bulb.Then the bulb is shorted out.The bulb is not damaged , but the wires can become hot enough to burn.

 Question: What is horse power and why is it called horse power? Answer: The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. We are also reminded of him every day when we talk about 60-watt light bulbs. What horsepower means is this: In Watt's judgment, one horse can do 33,000 foot-pounds of work every minute. checkout this very interesting link regarding story behind horsepower.

 Question: Define Atomic Structure. Answer: Atoms consist of negative charges (electrons) revolving around the nucleus, which itself consists of positive charges (protons) and neutral particles (neutrons). Number of electrons and a proton in an isolated atom remain equal and are called Atomic Number of that atom. Hence the equal negative charge shields the positive charge at the center and atom as a whole become neutral. According to the quantum theory of atoms, energies, referred as energy levels, of electrons in an isolated atom are not continues but discrete. This means that electrons require certain minimum amount of energy to increase their energy level, or in other words they can’t increase their energy unless they are given that minimum energy. Check out this very interesting discussion regarding energy levels.

 Question: What is Luminous intensity? Answer: Luminous intensity is an expression of the amount of light power emanating from a point source within a solid angle of one steradian. For reference, a frequency of 540 terahertz (540 THz or 5.40 x 1014 Hz) is specified. The quantities used to express luminous intensity are arcane to most non-scientists. A frequency of 540 THz corresponds to a wavelength of about 555 nanometers (nm), which is in the middle of the visible-light spectrum, and is generally accepted as the frequency and wavelength at which the average human eye is most sensitive. A steradian is the standard unit solid angle; a sphere encloses 4p (approximately 12.57) steradians.Decades ago, luminous intensity was measured in terms of a unit called the candle. This expression arose from the fact that one candle represented approximately the amount of visible radiation emitted by a candle flame. This was an inexact specification, because burning candles vary in brilliance. So, for a time, a specified amount of radiation from elemental platinum at its freezing temperature was used as the standard. Late in the 20th century, the candela was defined and adopted as the standard unit of luminous intensity. One candela (1 cd) is the magnitude of an electromagnetic field (EM-field), in a specified direction, that has a power level equivalent to a visible-light field of 1/683 watt (1.46 x 10-3 W) per steradian at 540 THz.

 Question: What are Insulators? Answer: Material in which electrical charges do not move freely from place to place. (wood, paper, plastic, glass, rubber).

 Question: What is Centripetal force and centrifugal force? Answer: Centripetal force and centrifugal force, action-reaction force pair associated with circular motion. According to Newton's first law of motion, a moving body travels along a straight path with constant speed (i.e., has constant velocity) unless it is acted on by an outside force. For circular motion to occur there must be constant force acting on a body, pushing it toward the center of the circular path. This force is the centripetal (center-seeking) force. For a planet orbiting the sun, the force is gravitational; for an object twirled on a string, the force is mechanical; for an electron orbiting an atom, it is electrical. The magnitude F of the centripetal force is equal to the mass m of the body times its velocity squared v 2 divided by the radius r of its path: F=mv2/r. According to Newton's third law of motion, for every action there is an equal and opposite reaction. The centripetal force, the action, is balanced by a reaction force, the centrifugal (center-fleeing) force. The two forces are equal in magnitude and opposite in direction. The centrifugal force does not act on the body in motion; the only force acting on the body in motion is the centripetal force. The centrifugal force acts on the source of the centripetal force to displace it radially from the center of the path. Thus, in twirling a mass on a string, the centripetal force transmitted by the string pulls in on the mass to keep it in its circular path, while the centrifugal force transmitted by the string pulls outward on its point of attachment at the center of the path. The centrifugal force is often mistakenly thought to cause a body to fly out of its circular path when it is released; rather, it is the removal of the centripetal force that allows the body to travel in a straight line as required by Newton's first law. If there were in fact a force acting to force the body out of its circular path, its path when released would not be the straight tangential course that is always observed.

 Question: What is the difference between open and closed ciricuit? Answer: OPEN CIRCUIT:    When any part of the path is broken, the circuit is open because there is no continuity in the conducting path. The resistance of an open circuit is infinitely high. The result is no current in open circuit. CLOSED CIRCUIT    is a circuit which provides complete or continuous path for current flow., in other words current flows from one side of the applied voltage source, through the external circuit, and returns to the other side of voltage source. in closed circuit there must be a resistance in the path of current.

 Question: What is the difference between resistance and conductance? Answer: RESISTANCE is the opposition to current flow. Its unit is ohm. Resistors are perhaps the most common component in electronic circuits. Their main function is to reduce the current I to the desired value or to provide the desired voltage in a circuit CONDUCTANCE is the ability to conduct current. It is the reciprocal of resistance=I/R. The unit is the Siemens's).

 Question: Define Potential difference and Current. Answer: Current (measured in Amperes) is actually the flow of electrons (charge). Its like finding the quantity of water flowing through a pipe of certain area in unit time. So imagine the cross-section of a wire having electrons passing through. Now if you count the no. of electrons passing through the cross-section in one second that would be exactly the quantity what is called current? A volt is the measure of Potential Difference across circuit elements (battery, resistor etc.). Consider two cylinders of water one having less water than other, now link the two cylinders with a pipe, so that the water from one cylinder can pass to other. Now what will be the direction of water?....... YES. you are right. water will flow from the cylinder having more water to one that has less water. this will result in decreasing of water level from where it is flowing and increase in water level in cylinder to which water is flowing. When both levels come to same height, water will stop to flow. Technically this happens due to the difference in the potential energies of water in two cylinders. Water will flow only when there is a potential difference, and when it is zero (i.e. when two levels become equal) water will stop to flow. Same thing happens when we create a potential difference across a wire, on one side of wire there are more electrons, creating a negative charge region, while on the other end electronic concentration is low, becoming a positive region as compared to the negative region. This potential difference will make electrons to flow from negative to the positive side. thus resulting in non zero current. In case of zero potential difference (i.e. when both side have equal no. of electrons making the two sides at the same potential), no electron will feel a 'push' to either end, thus results in zero current. This is the basic relation between currents and volts, with currents acting as 'effect' and volts as 'cause'. Now since under applied voltages, electrons flow through wire, that means by applying voltages we give electric energy (measured in Joules) to the wire, Check this interesting link to get a deep insight into charge flow.

 Question: Please click below for practical tips in solving circuit problems Answer: Circuit Theory in a NutShell (practical tip

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