1) In electronics, a circuit is a path between two or more points along which an electrical current can be carried. (A circuit breaker is a device that interrupts the path when necessary to protect other devices attached to the circuit - for example, in case of a power surge.)

2) In telecommunications, a circuit is a discrete (specific) path between two or more points along which signals can be carried. Unless otherwise qualified, a circuit is a physical path, consisting of one or more wires (or wireless paths) and possibly intermediate switching points. A network is an arrangement of circuits. In a dial-up (switched) connection, a circuit is reserved for use by one user for the duration of the calling session. In a dedicated or leased line arrangement, a circuit is reserved in advance and can only be used by the owner or renter of the circuit.

3) A virtual circuit, sometimes called a logical circuit, is a path between two or more points that seems like a fixed physical path, but actually is one path out of many possible physical paths that can be arranged. A permanent virtual circuit(PVC) is a virtual circuit that provides a guaranteed connection between two or more points when needed without having to reserve or commit to a specific physical path in advance. This allows many companies to share a common pool of circuits. This approach is used in a frame relay network and offers a committed set of resources to a telephone company customer at a lower price than if the customer leases their own circuits. A switched virtual circuit (SVC) is similar to a permanent virtual circuit, but allows users to dial in to the network of virtual circuits.

EMF meters detect fields emitted by moving electrically charged objects. Electromagnetic field theory lies at the combination of an electric field, produced by a charged object, and the magnetic field created when the charged object moves. Scientists previously separated electric fields from magnetic fields, but a combination of the two fields models reality better.

Electromagnetic fields are created using alternating current and direct current, but with different results. EMF meters measure fields produced by alternating current the type of electricity surging through your microwaves and television. This current moves back and forth fifty to sixty times a second. Direct current fields are stationary, like the earth's magnetic field, and cannot be measured by most EMF meters (but that's okay, as it would essentially be background signal).

Day-to-day, EMF meters are used for diagnosis of problems with electrical wiring, power lines, and electrical shielding effectiveness, but professional ghost hunters swear by the inclusion of an EMF meter in their toolkits.

Kirchhoff Current Law and Kirchhoff Voltage LawUnder Basic Electrical

Kirchhoff's LawsThere are some simple relationships between currents and voltages of different branches of an electrical circuit. These relationships are determined by some basic laws that are known as Kirchhoff laws or more specifically Kirchhoff Current and Voltage laws. These laws are very helpful in determining the equivalent electrical resistance or impedance (in case of AC) of a complex network and the currents flowing in the various branches of the network. These laws are first derived by Guatov Robert Kirchhoff and hence these laws are also referred as Kirchhoff Laws.

Kirchhoff's Current LawIn an electrical circuit, the current flows rationally as electrical quantity. As the flow of current is considered as flow of quantity, at any point in the circuit the total current enters, is exactly equal to the total current leaves the point. The point may be considered anywhere in the circuit.

Suppose the point is on the conductor through which the current is flowing, then the same current crosses the point which can alternatively said that the current enters at the point and same will leave the point. As we said the point may be anywhere on the circuit, so it can also be a junction point in the circuit. So total quantity of current enters at the junction point must be exactly equal to total quantity of current that leaves the junction. This is the very basic thing about flowing of current and fortunately Kirchhoff Current law says the same. The law is also known as Kirchhoff First Law and this law stated that, at any junction point in the electrical circuit, the summation of all the branch currents is zero. If we consider all the currents enter in the junction are considered as positive current, then convention of all the branch currents leaving the junction are negative. Now if we add all these positive and negative signed currents, obviously we will get result of zero. The mathematical form of Kirchhoff's Current Law is as follows,

We have a junction where n number of beaches meet together.Let's I1, I2, I3, ...................... Im are the current of branches 1, 2, 3, ......m andIm + 1, Im + 2, Im + 3, ...................... In are the current of branches m + 1, m + 2, m + 3, ......n respectively.

The currents in branches 1, 2, 3 ....m are entering to the junction. Whereas currents in branches m + 1, m + 2, m + 3 ....n are leaving from the junction.

So the currents in the branches 1, 2, 3 ....m may be considered as positive as per general convention and similarly the currents in the branches m + 1, m + 2, m + 3 ....n may be considered as negative.

Hence all the branch currents in respect of the said junction are -

+ I1, + I2, + I3,................+ Im, Im + 1, Im + 2, Im + 3, .................. and In.

Now, the summation of all currents at the junction is-

I1 + I2 + I3 + ................+ Im Im + 1 Im + 2 Im + 3.................. In.

This is equal to zero according to Kirchhoff Current Law.

Therefore, I1 + I2 + I3 + ................+ Im Im + 1 Im + 2 Im + 3.................. In = 0.

The mathematical form of Kirchhoff First Law is I = 0 at any junction of electrical network. Kirchhoff's Voltage Law

This law deals with the voltage drops at various branches in an electrical circuit. Think about one point on a closed loop in an electrical circuit. If someone goes to any other point on the same loop, he or she will find that the potential at that second point may be different from first point. If he or she continues to go to some different point in the loop, he or she may find some different potential at that new location. If he or she goes on further along that closed loop, ultimately he or she reaches the initial point from where the journey was started. That means, he or she comes back to the same potential point after crossing through different voltage levels. It can be alternatively said that net voltage gain and net voltage drops along a closed loop are equal. That is what Kirchhoff Voltage law states. This law is alternatively known as

Kirchhoff Second Law.If we consider a closed loop conventionally, if we consider all the voltage gains along the loop are positive then all the voltage drops along the loop should be considered as negative. The summation of all these voltages in a closed loop is equal to zero. Suppose n numbers of back to back connected elements form a closed loop. Among these circuit elements m number elements are voltage source and n - m number of elements drop voltage such as resistors.

The voltages of sources are V1, V2, V3,................... Vm.

And voltage drops across the resistors respectively, Vm + 1, Vm + 2, Vm + 3,..................... Vn.

As it is said that the voltage gain conventionally considered as positive, and voltage drops are considered as negative, the voltages along the closed loop are -

+ V1, + V2, + V3,................... + Vm, Vm + 1, Vm + 2, Vm + 3,..................... Vn.

Now according to Kirchhoff Voltage law, the summation of all these voltages results to zero.

That means, V1 + V2 + V3 + ................... + Vm Vm + 1 Vm + 2 Vm + 3 + ..................... Vn = 0.

So accordingly Kirchhoff Second Law, V = 0.

Application of Kirchhoff's Laws to CircuitsThe current distribution in various branches of a circuit can easily be found out by applying Kirchhoff Current law at different nodes or junction points in the circuit. After that Kirchhoff Voltage law is applied, each possible loop in the circuit generates algebraic equation for every loop. By solving all these equations, one can easily find out different unknown currents, voltages and resistances in the circuits.

Some Popular Conventions We Generally use During Applying KVL1) The resistive drops in a loop due to current flowing in clockwise direction must be taken as positive drops.2) The resistive drops in a loop due to current flowing in anti-clockwise direction must be taken as negative drops.3) The battery emf causing current to flow in clockwise direction in a loop is considered as positive. 4) The battery emf causing current to flow in anti-clockwise direction is referred as negative.

Series and Parallel CircuitsSeries circuitsA 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:

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 circuitsA 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:

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 AI2= 10 / 8 = 1.25 AI3=10 / 4 = 2.5 ANote that the currents add together to 5A, the total current.

Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.

Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is generally supplied to businesses and homes by the electric power industry through an electric power grid. Electric power is usually sold by the kilowatt hour (3.6 MJ) which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a running total of the electric energy delivered to a customer.