BE Circuit Concepts

8/10/2019 BE Circuit Concepts

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Unit 1 : Circuit Concepts


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Electrical Quantities

Charge and Electric Force :

There are two types of charge:

1. Positive.

2. Negative.

The electric charge is an invisible property acquired by matter that by the interactions it produces.

All matter (solids, liquids, and gases) are made of atoms.An atom is

of electrons, protonsand neutrons.


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Electrons have a negative chargewhile protons have a positive cha

have no electric charge.

The amount of negative charge on an electron

is exactly equal to the amount of (opposite)positive charge on a proton.

Charges that are same (or like) repel each other.

Charges that are different (or unlike) attract each

other.

The fundamental unit of charge is the coulomb (C).

A single electron has a charge

of1.6021019

C and a single proton has a charge of+1.6021019

C.


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Coulomb's Law :

Coulomb's law states that the electrical force between two charged

directly proportional to the product of the quantity of charge on thinversely proportional to the square of the separation distance betw

objects.

where q1 = quantity of charge on object 1 (C) ,

q2 = quantity of charge on object 2 (C) and

d = distance between the two objects (in

meters)


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Current is moving positive electrical charge.

Measured in Amperes (A) = 1 Coulomb/s. Current is represented

In general, current can be an arbitrary function of time.

Constant current is called direct current (DC).

Current that can be represented as a sinusoidal function of time

contexts a sum of sinusoids) is called alternating current (AC).

Current :


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Voltage is electromotive force provided by a source or adifference between two points in a circuit.

Measured in Volts (V): 1 J of energy is needed to move

through a 1 V potential difference.

Voltage is represented by V or v.

Voltage:


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Potential difference (V) :

Potential difference is the work done per unit charge. A potential d

means that 1 joule of work is done per coulomb of charge. ( 1 V = 1

Potential difference in a circuit is measured using a voltmeter which

parallel with the component of interest in the circuit.

V = potential difference in volts, V

W = work done or energy transferred in joules, J

Q = charge in coulombs, C


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Power :

Power is defined as the time rate of change of doing work. We exp

dwp

dt

We can write equation as follows:

dw dqp vi

dq dt

Power has units of watts.


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Electrical energy is defined as the product of Powerand

Therefore unit of energy will be watt-hour or Joules.

E = P x t

The energy is the area under the power-time curve.

Energy is also defined as capacity to do work.

Energy :


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Ideal independent voltage source :

An ideal dependent voltage source is characterized as having a cons

across its terminals, regardless of the load connected to the termin

The ideal voltage source can supply any amount of current. Further

independent voltage source can supply any amount of power.

The standard symbols of the ideal independent voltage source are s

+_v(t) E

Sometimes

used

Most often

used


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Ideal independent current sources :

An ideal independent current source is characterized as providin

value of current, regardless of the load.

If the current source is truly ideal, it can provided any value of vo

amount of power.

The standard symbol used for the ideal independent current sou

below.

i(t) 1 meg1 amp

+

-

V

V = ?


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Dependent voltage source :

A dependent voltage source is characterized by depending ona volt

somewhere else in the circuit.

The symbol for the current source is shown below. Note the diamo

A circuit containing a dependent voltage

source is shown below :

10

30

+_5 V 10

A circuit with a current controlled dependent

voltage source.


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Dependent current source :

A dependent current source is characterized by depending on a vol

somewhere else in the circuit. The symbol for a dependent current

shown as follows:

10

+5 V 4vx_

A circuit containing a dependent current

source is shown below :

A circuit with a voltage controlled dependent

current source

W f


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Waveforms :

A Waveform is a graph of magnitude of quantity w.r.t time.

The quantity plotted on X-axis is time and on Y-axis is voltage ,c

power , etc.

The shape of an A.C quantity such as current , voltage or power

a sinwave always.

The figure of sinusoidal waveform is as follows :

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BE Circuit Concepts