Applied Electricity Concise Notes for Senior High Schools (SHS 1, 2 & SHS 3)

 

Introduction to Electricity 

Electricity is the flow of electrons (charges) through a pathway that conducts electricity (conductor). 

Electronics is the study of precisely controlling the flow of electrons. 

Applied Electricity is the practical application of electrical and electronic concepts, principles or theories in solving electrical problems. 

 

Differences Between Electricity and Electronics 

ELECTRICITY

ELECTRONICS

It deals with only the flow of electrons.

It deals with the control of the flow of electrons.

It is limited to the direct effect of flow of electrons through a pathway.

It is not limited to the direct effect of flow of electrons through a pathway.

Electricity is usually the study of high voltage.

Electronics is usually the study of low voltage.

 

Similarities Between Electricity and Electronics 

(1)   Both deal with the flow of electrons through a conductor.

(2)   The flow of electrons causes effect on both.

 

Nature Of Electricity Nature Of Electricity

When two surfaces are moved over each other several times, charge is produced. Charged objects may attract small bits of papers or other lightweight materials. Since electric charge is confined in an object, it is said to be electrostatic charge. 

Electrostatics: It is defined as the electric charge at rest. The law of electrostatics states that  

v  Like charges repel  

Law of electrostatics

v  Unlike charges attract                                 

Law of electrostatics

Static Electricity: It is produced by friction between two surfaces in close contact. E.g. Lightning

Current Electricity: It is produced when an electric charge is in motion. E.g. Starting a car, turning on a light, charging a cell phone. 


Energy Level Diagram 


Energy level is the fixed amount of energy that a system described by quantum mechanics.

Energy band is a narrow range of energy corresponding to a certain energy level.

Conduction band: Electrons are separated from their parent atoms and free to move throughout the solid (assembly of atoms). Conduction band is the highest energy band and its electrons have the greatest mobility.

Valence band: Electrons are tightly bound to the individual parent atoms. It is the lowest energy band and its electrons are not free to move.

Forbidden band: There are no electrons present in this energy band. It is the gap between the valence band and the forbidden band.

 


CONDUCTORS

The conduction band and valence band are completely filled. The conduction band also overlaps with the valence band and thus no forbidden band is present. 

The conduction band and valence band are completely filled. The conduction band also overlaps with the valence band and thus no forbidden band is present.

energy band

Effect of Temperature on Conductors

Increasing temperature of a conductor increases its resistivity and reduces its conductivity.

 

INSULATORS

The valence band is completely filled but conduction band is completely empty. Therefore, it has wider forbidden band and negligible electrical conductivity. 


energy band
Insulators


Effect of Temperate on Insulators

When temperature is increased in insulators, electrons breakaway becoming free electrons and therefore increasing the conductivity insulators.

Semiconductors

The valence band is completely filled but partially filled conduction band. Due to this, its forbidden band narrows.


Effect of Temperature on Insulators

When temperature is increased in insulators, electrons breakaway becoming free electrons and therefore increasing the conductivity insulators.


SEMICONDUCTORS 

The valence band is completely filled but partially filled conduction band. Due to this, its forbidden band narrows. 


energy band
Semiconductors



EFFECT OF TEMPERATURE ON SEMICONDUCTORS 

Increasing temperature of a semiconductor increases its electrical conductivity. The conductivity of a semiconductor is controlled by temperature and impurities. 


Temperature's Impact on Electrical Conductivity

Semiconductors have a unique property where their conductivity increases with temperature. This is opposite to metals, whose conductivity decreases with rising temperature.

Intrinsic Semiconductors: In intrinsic (pure) semiconductors, increasing the temperature provides enough energy to break some of the covalent bonds, releasing more charge carriers (electrons and holes). This increases the material's electrical conductivity. The relationship can be described using the equation:

σ∝T3/2e−Eg2kT\sigma \propto T^{3/2} e^{-\frac{E_g}{2kT}}

σ∝T3/2e−2kTEg​​

where 
σ\sigmaTTEgE_gkk

- Extrinsic Semiconductors: In extrinsic semiconductors, which are doped with impurities to increase charge carriers, temperature also affects conductivity. At low temperatures, dopant atoms are less ionized, leading to fewer charge carriers. As temperature rises, more dopant atoms ionize, increasing the number of free electrons or holes. However, at very high temperatures, intrinsic carrier generation becomes significant, and the semiconductor behaves more like an intrinsic one.


Carrier Mobility

Carrier mobility refers to how quickly electrons and holes can move through the semiconductor material. Higher temperatures increase phonon scattering, reducing the mobility of charge carriers. Therefore, while higher temperatures can increase the number of charge carriers, they also reduce their mobility, affecting the overall conductivity in complex ways.


Leakage Currents

Temperature increases can also lead to higher leakage currents in semiconductor devices. Leakage currents are unwanted currents that flow even when the device is supposed to be off. This can be particularly problematic in integrated circuits and can lead to higher power consumption and reduced efficiency.


Thermal Runaway

In some semiconductor devices, like transistors, an increase in temperature can cause a further increase in current, leading to more heat generation. This positive feedback loop, known as thermal runaway, can damage the device if not properly managed.


Applications and Considerations

Understanding the temperature effects on semiconductors is crucial in designing and operating electronic devices. It impacts everything from the performance of solar cells and LEDs to the reliability of computer processors and other integrated circuits.

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