Resistors

are components manufactured to possess a specific value of resistance to the flow of current. it is the most commonly used component in an

electronic circuit. 

Resistors are available with fixed or variable resistance values. They are available in a variety of shapes and sizes to meet specific

circuit, space, and operating requirements

series and parallel configuration

series circuit contains two or more resistors and provides one path for current to flow. The current flows from the negative side of the voltage source through each resistor to the positive side of the

voltage source. If there is only one path for current

to flow between two points in a circuit, the

circuit is a series circuit.

The more resistors connected in series, the more opposition there is to current flow. The more opposition there is to current flow, the higher the resistance in the circuit. In other words, when a

resistor is added in series to a circuit, the total resistance

in the circuit increases. The total resistance in a series circuit is the sum of the individual resistances in the circuit. 

parallel circuit contains two or more resistors and provides two or more paths for current to flow. Each current path in a parallel circuit is called a branch. The current flows from the negative side

of the voltage source, through each branch of the parallel circuit, to the positive side of the voltage source. 

If there is more than one path for current to flow between two points in a circuit with two or more resistors, the circuit is a parallel circuit.

The more resistors are connected in parallel, the less opposition there is to current flow. The less opposition there is to current flow, the lower the resistance in the circuit. In other words, when a resistor is added in parallel to a circuit, the total resistance in the circuit decreases, because additional paths for current

flow are provided. In a parallel circuit, the total resistance is always less than the resistance of any branch.

Electrical Resistance

The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor

Factor that affect the Resistance of the conductor

1-Length of the conductor

The first factor that affect the resistance is the length of the conductor ,if we have two conductor the first is shorter than the other , the resistance

2-cross sectional area

The conductor on the left has a wide cross sectional area than the rit ad therefore the resistance on it would be less because the current has a wide area for flow

3-Resistivity

    Is a fundamental property that quantifies how strongly a given material opposes the flow of electric current 

 measure in ohm.meter

 Resistance Measurement

The SI unit of electrical resistance is the ohm (?), while electrical conductance is measured in siemens (S).

Electric Cells

Electric cell is  cell contain a positive and a negative electrode separated by an electrolytic solution

Types of cell

There are two basic types of cells.

primary cells : Cells that cannot be recharged are called . Cells

secondary cells :that can be recharged are called 

Series Configuration of Cell

In a series-aiding configuration, the positive

terminal of the first cell is connected to the negative

terminal of the second cell; the positive terminal

of the second cell is connected to the

Total  Voltage produced equal the sum of the individual cell voltages and the     Same current flow through  the cells

Parallel configuration of Cell

In a parallel configuration, all the positive terminals

are connected together and all the negative

terminals are connected together .

The total current available is the sum of the individual

currents of each cell or battery.

•       The total voltage is the same as the voltage of each individual cell

•       The total current available is the sum of the individual currents of each cell

Electric Current

An electric current is a flow of electric charge 

The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second.

Measurement of electric charge 

To measure electric charge we use

1-coulumb

2-electron

But we usually muse column

Single electrons have a charge too small for

practical use. The unit adopted for measuring

charges is the coulomb

electric current

is the flow of negative charges. Scientists and engineers once thought that current flowed in a direction opposite to electron

flow

Hole

When  an electron from one atom to the next created

the appearance of a positive charge, called a hole,

moving in the opposite direction

Voltage

voltage is Electric potential differences between points can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three

A current is produced when an electron is forced from its orbit around an atom.

Any form of energy that dislodges electrons from atoms can be

used to produce current.

 Voltage Source 

The six most common voltage sources

1- friction

2- magnetism

3- chemicals

4- light

5- heat

6-pressure.

note :-

voltage may represent either a source of energy (electromotive force) or lost, used, or stored energy (potential drop)

Unit of Measurement

voltage  measured in joules per coulomb (volts).

Introduction to electrical engnineering

Electrical engineering is a professional engineering discipline that generally deals with the study and application of electricity, electronics, and electromagnetism