Fundamentals of Electricity

fundamentals of electricity and electronics | current

 Chapter objectives:

At the end of the chapter, you will be able to:

•  Define electricity
•  Define voltage and current
•  Describe the Bohr’s Model of Atom
•  Explain the concept of Direct and Alternating current
•  Identify advantages and disadvantages of Alternating current and Direct current
• Explain the use of AC and DC in computer
•  Measure voltage and current using multi meters
•  Identify Voltage and current requirements in a PC

Recall:

In the previous chapter, you have learnt that Microsoft Office PowerPoint takes an essential and innovative new approach to its user interface that enables you to create better presentations quickly as compared to the earlier versions of PowerPoint. When you start PowerPoint Application using the Start menu, by default it creates a new blank presentation with one slide and filename as Presentation1 until you save it with some other name. Power Point allows you to insert WordArt, picture and theme on the slide in your presentation.

1. Write down the steps save the Power Point slide?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

2. Write down the steps to format an existing PowerPoint presentation.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….

Voltage and current are two different terms. Voltage is the force due to which electrons flow in circuit i.e. current. In other words, we can say voltage is the cause and current is effect.

 6.1 What is electricity?

Electricity is the general term we have known for years. Basically, it is a naturally occurring force which is around us. But it has scientific concepts as well. We can say that electricity is a form of energy with the flow of electrons and protons which results in the flow of electric charges.

In nature s lightning is the best example of electricity. There are certain terms related to electricity like electric charge, electromagnetism, electric current, electric potential, electric field.

Electric charge depends upon the flow of electric current which consists of electrons flowing from negative to positive terminal of the battery. Whenever a unit of electric charge is moved from one point to another, the electric potential is measured. The space where it is surrounded by electrically charged particles is known as electric field. These charged particles interaction causesel  ectromagnetic fields.

 6.1.1 Define Voltage:

Voltage can be defined as the measure of potential difference (the difference in electric potential between two points) or electromotive force (commonly known as EMF is that causes current to flow)

Voltage is measured by voltmeter. The SI unit of voltage is volts. It is represented by  symbol “V” OR “E

 6.1.2 Define Current:

Current is defined as the flow of electrical charge from one point to another. The flow of current occurs when the electrons flow from negative polarity to the positive  polarity of the voltage source. But, it is globally accepted that the current direction is from the positive terminal to the negative terminal of voltage source.

Current is measured in amperes. It is represented by symbol “I”. Current is measuredby ammeter.

 6.2 Understanding Bohr’s Model of Atom:

Niels Bohr proposed this model in early 1900s.This model describes an atom as Positively charged particles where an electron revolves around nucleus in circular orbits. An atom can be broken up into small particles namely electrons, protons and neutrons.

Each of these particles possesses different characteristics. Figure 6.1 shows the combination of three particles for the formation of atom.

Figure 6.1 Bohr Model of Helium Atom

Figure 6.1 shows a helium atom where two protons and two neutrons are combined together near the center of the atom. The center part of the atom is called as nucleus of the atom. The neutrons and protons have approximately the same weight and size. The overall weight of the atom is determined by the number of protons and neutrons in the nucleus.

In an atom, the electrons rotate around the nucleus. In Figure 6.1, the helium atom has two electrons. These electrons are extremely light in weight and travel at a higher speed. You can compare the atom to the solar system with the nucleus representing the sun and the electrons representing the planets. The electrons rotate around the nucleus in the same way as the planets orbit around the sun.

It is interesting to note that no one has ever seen an atom because of its small size. Hence, any picture of the atom is based on assumptions rather than actual observation. Figure 6.1 is a very simple model though complex models have been proposed. However, the common thing in all these models is that they all assume that the basic structure consists of electrons orbiting around nucleus that is largely composed of protons and neutrons.

 6.2.1 Atom

Atom is an essential piece of matter which consists of nucleus in the centre which is surrounded by electrons. It is made up of three basic particles namely; electrons

protons, and neutrons where protons carry positive charge. electrons carry negative charge and neutrons are neutral in charge. Electrons in an atom are bound by electromagnetic force to the nucleus. Thus, a molecule is formed by the group of atom

An atom which contains equal number of protons and electrons are neutral in charge, or else they have positive or negative charge. The nucleus consists of numbers of protons and neutrons where number of protons helps to determine chemical element which strongly influence the magnetic properties of an atom and the number of neutrons helps to determine an isotope of the element.

 6.3 Concept of Direct and Alternating Current

In an alternating current, the flow of an electric charge switches periodically back and forth whereas in direct current it flows smoothly in one direction. The current which flows through the power lines and household appliances are alternating current and current that flows through batteries are direct current.

The only advantage of using alternating current is that it is cheap for changing the voltage of the current. Further, the loss which is experienced when current is carried over long distances is less as compared to the direct current.

 6.3.1 Direct Current

The electric charge that flows smoothly in one direction is called as Direct current.These current are generated by using sources like solar cells, batteries, etc. It flows in conductor like wire as well as through semiconductors, insulators, vacuum etc. Previously, direct current also referred to as Galvanic current.

We can obtain direct current from alternating current as well by using a device called rectifier which has electronic or electromechanical elements that allows electric charge to flow in one constant direction. Figure 6.2 shows the Direct Current waveform

Figure 6.2 Direct current waveform

6.3.2 Alternating current

The electric charge that periodically switches the direction back and forth is known as alternating current. The electric charge in alternating current for instance moves forward then backward and vice versa These current are mainly used in householdand businesses

Normally, alternating current is represented in sine waveform but sometimes it appears in triangular or square waveforms in few appliances and in few cases it appears very complicated. The bestexample of alternating current is audio and radio signals which carries on electrical wires.

The voltage required by an AC power source can be transformed with the help of power transformer due to which the voltage is increased for distribution or transmission. But the voltage of AC power source changes frequently. Figure 6.3 shows Alternating Current waveform

Figure 6.3-Alternating current waveform

 6.3.3 Advantages of Direct current

•  In DC system, the frequency is zero hence there are no variations and even connection synchronization is also not necessary.

•  In DC, there are no issues of maintaining the stability and security of the system it means the transmission of power is easy.
• In DC system it has lower line resistance and hence it has less loss.
•  It never induces reactance in the line. This results in translation of higher power capability and capacity.

6.3.4 Disadvantages of Direct current

• Power is lost during the transmission of electric charge through wire due to resistance of the wire.
•  It is less reliable and available in case of HDVC (high voltage direct current)
• It is possible to convert the DC into AC but it is too complex and costly.

6.3.5 Advantages of Alternating Current

•  An AC voltage can be easily transformed to a higher or lower voltage by passing it through a simple device known as transformer which can be achieved with very less loss of power.
•  Alternating current can be converted into direct current very easy and can be made available to the DC equipment’s.

 63.6 Disadvantages of Alternating Current

• Alternating current requires transformers in their AC generators which complicates their circuits.
•  Due to higher voltage there are safety related issues in which it increases risk of an electric shock
• It is expensive to transmit electric charges for long distances.

 6.4 Use of AC and DC

AC and DC both are applied for the various usage but generally, we prefer AC over DC as the voltage can be transformed easily in AC. AC is mostly used for the household appliances like computers, television, bulbs etc. and businesses purposes whereas DC is required for electronic components.

 6.4.1 Use of alternating current and direct current in computers

Computers has switch mode power supply plugged to it that supplies power to the computers. Before providing the power to all components, switch mode power supply converts alternating current into direct current which is then provided to the various components of computers like hard disk, DVD drive, Processor, Keyboard, mouse etc

In computers these power supplies help in providing sufficient amount of voltage required by these components. For example we can say that the required supply by motherboard, disk drives is upto +5V (+-5%) and tens of amperes is supplied by power supply.

It always depends upon the PC model, the power supply is provided in between 150 and 350 watts.

6.4.2 Measuring of voltage using voltmeter

Voltmeter measures the potential difference between two points i.e. positive and negative terminal. Whenever we need to determine the voltage its ends are connected to that point. Its first terminal will provide us some voltage reading and some other reading at another end. Then the difference between two ends is shown as an actual voltage.

Now, let us see how voltage is measured using voltmeter. The following figure depicts  the idea for the same.

Figure 6. 4 – Measuring of voltage using voltmeter

 In the figure 6.4, we measure voltage across the V4. It’s important to maintain the terminals polarity because if connect the terminals opposite to the given polarity the voltage measured will be negative across V4.

 6.4.3 Measuring of current using ammeter

Ammeter measures the current across the circuit. Current which has smaller values  are measured using milliameter or microammeter. It has basic component as galvanometer which shows the deflection proportional to the electric charge which passes through it. Now, let us see how we measure the current. The following figure depicts the idea of measuring current through ammeter.

Figure 6.5 Measurement of current using ammeter

Fiqure 6.5-(A) Depicts the complete circuit where we need to measure the current. The easiest way to measure the current in a circuit is by plugging in ammeter in series (i.e. in line) along with the circuit.

Figure 6.5 (B) and (C) depicts how we remove power by disconnecting one side of battery and breaking the circuit at point where current is to be measured.

Figure 6.5 (D) depicts that ammeter is connected in series over the point where weneed to measure the current

Figure (E) depicts the complete circuit where current is flowing and readings are taken by the ammeter.

 6.5 Voltage and Current requirements in a PC

Voltage required by PC is 330V and normal current requirement is 3.3A. If your system has lot of drives current required will be +13A and if you use more than one CPU then rating will be +3.3A and +5A.

Summary:

• Electricity is a form of energy with the flow of electrons and protons which resultsin the flow of electric charges.
• Voltage can be defined as the measure of electromotive force or potential difference.
• Current is defined as the flow of electrical charge from one point to another.
• Bohr model describes the atom as the smallest part of an element. It consists of protons and neutrons at its centre and the electrons revolving around them.
• In an alternating current, the flow of an electric charge switches periodically back and forth whereas in direct current it flows smoothly in one direction.
• AC is used in household appliances and businesses whereas DC is applied are produced by batteries and solar cells.
• Voltmeter measures the potential difference between two points i.e. positive and negative terminal.
• Ammeter is a device used for measuring flow of electric current in a circuit.

Quiz:

 Fill in the blanks:

• The force which sets the electrons into motion is called as ……………………………………

1. Potential Difference
2. Voltage
3. EMF
4. Ampere

• The ………………. and………….. Have approximately the same weight and size.

1. Neutrons, Protons
2. Protons, Electrons
3. Electrons, Neutrons
4. Electrons, Nucleus

• The……………..is used for measuring voltage.

1. Ohmmeter
2. Galvanometer
3. Voltmeter
4. Ammeter

HANDS ON 1: MEASURING VOLTAGE USING A MULTIMETER IN A GIVEN CIRCUIT

 OBJECTIVE:

To measure voltage using a multimeter in a given circuit

MATERIAL REQUIRED:

• Multimeter
• Plug point to measure voltage and power supply (SMPS +3.3V, +5V, +12V)
• Hook-up wires

Figure 6.6- Voltage measure using multimeter from SMPS

PROCEDURE:

1. Similarly connect the positive terminal and negative terminal of multimeter to SMPS
2. Turn the trainer kit on the measure the voltage.
3. V1=_____________________ Volts.

HANDS ON 2: MEASURING THE VOLTAGE OF A BATTERY USING A MULTIMETER

 OBJECTIVE

To measure voltage of a battery using a multimeter.

MATERIAL REQUIRED:

• Multimeter
• Battery
• Hook-up wires

Figure 6.7- Voltage measure using multimeter of battery

 PROCEDURE:

1. Connect the positive terminal of terminal of battery to multimeter (DC voltage).
2. Similarly connect the negative terminal of battery to multimeter.
3. And take the reading flashed in multimeter.
4. Voltage V1 =________________Volts

HANDS ON 3: MEASURING THE CURRENT FLOWING A CIRCUIT USING MULTIMETER

OBJECTIVE:

To measure current using a multimeter in a given circuit.

 MATERIAL REQUIRED:

• Digital Multimeter
• Hook-up wires

Figure 6.8- Current measure using mulitmeter

 PROCEDURE:

1. Connect the positive terminal of digital multimeter to the battery.
2. Similarly connect the negative terminal.
3. Take the readings flashed in multimeter.
4. I=______________ Ampere