basic electrical technology questions with answers

Balochistan University Of Information Technology, Engineering and Management Sciences, Quetta

Faculty of EngineeringDepartment of Mining Engineering

AssignmentClass: BS (Mining) Semester 3rd Date: 27.12.2013

Course: Basic Electrical Technology Instructor: Muhammad Bux

Name: Ghulam Mehdi Roll No: 23101

Q.1: Explain the different types of First Aid.Ans: Emergency treatment given before regular medical services can be obtained is known as First Aid.There are six types of First Aid Training.

1 . First Aid & Cardio-pulmonary Resuscitation: First Aid and Cardio-Pulmonary Resuscitation are the most common first aid training that everyone should learn, whether you are a teenager or a senior citizen, whether you are an office worker or a business owner.In this first type, one should learn about the different techniques such as Cardio-pulmonary Resuscitation protocols, caring for open wounds, burns, and fractures. The use of Automated External Defibrillators may also be included in this training. As a matter of fact, most of the workplaces today require occupational first aid and Cardio-pulmonary Resuscitation trainings.2. Trainings for Sports Safety:This type of first aid training wanted to train individual to treat injuries that will happen in the sports fields, such as fractures, sprains, and contusions, to name a few. Also, sports safety trainings give appropriate instructions to minimize possible injuries to occur. Coaches and athletes are the most common audiences of this type of training. 3. First Aid Emergency:First aid emergency is a training that educates individual to help during emergencies such as providing utmost care for victims who may be seriously injured and the appropriate ways to do it. This type of training may also include Cardio-Pulmonary Resuscitation trainings. All can freely participate in this type of training especially those whose work are accompanied with many emergencies.4. Trainings for Babysitters:Training for babysitter is basically intended of older children, 11-15 years old. This involves basic first aid trainings for babysitting tasks.5. Children First Aid:In learning first aid, being young is not an excuse to learn care principles; you can enroll your kids in this type of training. Numerous first aid for children trainings are already designed for children who are five (5) years and above, these includes basic care principles that children can easily understand and apply.6. Pet First Aid:If you have pets at home and you love them so much, then consider this type of training and learn various ways in taking care for your little ones. This training teaches you how provide utmost care to your pets especially when they are choked, when they have wounds and sprained limbs.

Ghulam Mehdi CMSID@23101

http://www.medicore.ie/first-aid-training/first-aid-courses.html

http://www.medicore.ie/first-aid-training/first-aid-courses.html


If the person does not breathe then immediately arrange artificial method of breathing.There are three methods of artificial breathing.1-Holger Nelson Method:The victim should be kept in the bed facing the ground. Fold his hands & keep it in the backside of his head, the helper sitting at his head should massage his back using both hands. This is done with in two seconds.2-Mouth to mouth:In this method the helper pushes air by keeping his mouth on the victim’s mouth. By closing his nose then the air fills lungs. So the victim gets artificial respiration.3-Through Nose:In this method the helper send air through victim’s nose. By closing his mouth the air is blown in his nose till the heart of the victim rises by this way the victim gets artificial respiration. For a child the air blown is half the heart level, compared to adult.Q.2: Explain the properties of conductors and insulators.

Ans: Conductors are made of materials that electricity can flow through easily. These materials are made up of atoms whose electrons can move away freely. An object made of a conducting material will permit charge to be transferred across the entire surface of

the object. A conductor is a material which allows the easy passage of current through it. In a conductor the energy band gap is absent, that is, the valance and conduction bands overlap each

other. Hence even when a very small amount of energy is applied to the material the electron is excited from

the valance to conduction band. This results in the easy conduction of electricity. Some examples of conductors are:

Copper, Aluminum, Platinum, Gold,Silver,Water, People and Animals etc.

Insulators are materials opposite of conductors. The atoms are not easily free and are stable, preventing or blocking the flow of electricity. When a voltage is placed across an insulator, no current flows. Electrical insulation is the absence of electrical conduction. Insulators are characterized by having a large energy band gap. This is because the filled valence band

is very distant from the empty conduction band. For conduction to take place electrons must be transferred from the valance band to the conduction

band. Since the energy band gap is very high for insulators huge amount of energy has to be given to the material to excite an electron so that it reaches the conduction band.


Balochistan University Of Information Technology, Engineering and Management Sciences, Quetta Some examples of insulators are:

Glass,Porcelain,Plastic,Rubber etc.

Q.3: A resistor is connected in series with parallel circuit comprises of two resistances of 12 Ω and 8 Ω. Total power dissipated in the circuit is 70 watts when the applied voltage is 20 volts. Calculate value of resistance.Ans: Given Data:R1=12R2=8Power=70WVoltage=20VResistance(R) =?Sol:We know that in parallel circuit the resistance can find by:1/RT=1/ R1+1/ R2

Putting values’1/RT=1/12+1/8 =(2+3)/24 =5/24RT=24/5RT=4.8…………………Ans.

Q.4 What are the characteristics of primary and secondary cells? Ans:

o Primary Cells: oPrimary cells are the non-rechargeable cells

These cells produce electrical energy by themselves.

Once they are used up, they have to be discarded & can't be recharged.

In fact, their electrolyte can't undergo a reversible reaction. That is the reason it is not possible to

recharge them.


Balochistan University Of Information Technology, Engineering and Management Sciences, Quetta Their life is short.

They have low power output and low efficiency.

It has weightless and low cost.

Less maintenance required as compared to secondary cell.

Some examples are :

o Dry cells (Zinc-carbon cells),

o Leclanche cello Daniel cell.

o Secondary Cells: Secondary cells are rechargeable.

Their electrochemical reactions can be reversed.

Externally supplied electrical energy is stored in the form of chemical energy & the cell is "charged" and recharged again and again.



A secondary cell can undergo a limited number of such charge-discharge cycles. Their life is long. They have high power output and high efficiency.

It has heavy weight and costly.

High maintenance required as compared to primary cell.

Some examples are:o (i)-Lead acid battery,o (ii)-Li-ion battery,o (iii)-Ni-MH (Nickel metal hydride) battery.

Q.5 What defects occur in the secondary cell?Ans:There are Three types of defects occurs in the secondary battery. These are:

1-Sulphation.2-Sedimentation3-Plates buckling.1-Sulphation:Lead–acid batteries lose the ability to accept a charge when discharged for too long due to sulphation, the crystallization of lead sulfate.2-Sedimentation: When the particles deposited on the positive plate dissolves in the electrolyte, short circuit may occur. If it happens the electrolyte should be changed. 3-Plate Buckling:


http://en.wikipedia.org/wiki/Lead_sulfate


The plates become unshaped due to high rate of charging& discharging.

Q.6 Describe the working principle of alkaline cell.Ans: The main working principle of the alkaline batteries is based on reaction between zinc (Zn) and manganese dioxide (MnO2). Alkaline battery is so named because the electrolyte used in it is potassium hydroxide, a purely alkaline substance.In an alkaline battery cell, the powder zinc serves as anode, manganese dioxide serves as cathode and potassium hydroxide serves as electrolyte.

First half reaction is

Second half reaction is

Overall reaction


http://www.electrical4u.com/alkaline-batteries/


An alkaline battery cell is rated for 1.5 V. The average voltage under load condition may be 1.1 to 1.3 V. An alkaline cell is generally rated for 700 mA.

Q.7 What are the advantages and disadvantages of AC current?Ans:Advantages:

AC is easier to generate especially 3 phase for high power. With transformers it is easy to raise the voltage to higher levels which make the transmission easier. The higher voltage requires less current and would result in lower losses than higher current

transmission. AC can be more easily switched because the voltage is zero many times per second. All domestic appliances are designed to use AC. It can travel a farther distance than DC. The main advantage of AC is that it is more economical to transport.

Disadvantages:

Transmission lines have inductance and resistance which causes voltage drops and losses.

The inductance causes a voltage drop with AC.

Transmission lines that are as long as 10 percent (300 miles) or more of the 60 Hz wavelength (5,000 KM or 3,000 miles) radiate energy and thus have radiation losses.

60 Hz is the same frequency as the human body. It can kill you.

Q.8 What is difference between ammeter, voltmeter, ohmmeter and multimeter?Ans: Ammeter: An ammeter is an electrical instrument which is used to measure current in amperes.

Voltmeter: A voltmeter is an electrical instrument which is used to measure the potential difference in volts between two points. Ohmmeter: An ohmmeter is an electrical instrument which is used to measure resistance in ohms. Multimeter: A multimeter is an electrical instrument which is used to measure current in amperes, potential difference in volts and resistance in ohms.

Q.9 Discuss the working principle of moving coil instruments.Ans:Moining coil instruments:This type of instruments is based on the principle of permanent magnet moving coil mechanism i.e when a current carrying conductor is placed in a magnetic field, mechanical forces acts on the conductor. The coil placed in magnetic field and carrying current is attached to the moving system .With the movement of the coil the pointer moves over the scale.Construction: It consists of a powerful magnet with soft iron piece and light rectangular coil of many turns of fine wire wound on aluminum former inside which is an iron core .A permanent magnet provides a uniform magnetic field into which a spring-mounted moving coil is positioned. A pointer is attached to the moving coil. The current to be measured passes through the coil, which is free to pivot. As the current passes through the coil, it



produces a magnetic field that interacts with the uniform magnetic field produced by the permanent magnet. This interaction causes the moving coil and pointer to rotate.

Q.10 State the efficiency and protective devices of transformer.Ans :Transformer:

A transformer is a four-terminal device that transforms an AC input voltage into a higher or lower AC output voltage. Transformers are not designed to raise or lower DC voltages.

Efficiency of transformer:

Efficiency of a device is equal to the ratio of output to input. Since,


Balochistan University Of Information Technology, Engineering and Management Sciences, Quetta Output = Ps

or Output = Vs Isand

Input = Pp or Input = Vp Ip

Efficiency = output / input Efficiency = Ps / Pp Efficiency = Vs Is / Vp Ip Efficiency in percent = (Vs Is / Vp Ip) x 100.

In actual practice output is not equal to input therefore actual transformers are not 100% efficient. However commercial transformers have very high efficiency in the range of 95% to 99%.

There are four main protective devices of transformer which are given below:

1-Conservator

2-Breather

3-Explosion vent

4-Bucholz relay

1-Conservator:

The conservator is a cylindrical vessel. It is fitted on the top of the tank. Tank is filled with oil but conservator filled with oil partly.

2-Breather:

It is a small vessel. It is connected between conservator & air outlet. It contains silica gel. Silica gel color is blue when dry and pink when wet.

3-Explosion vent:

Explosion vent is fitted on the top of the tank .It protect the tank by the explosion and high pressures of gases. Under normal condition air is not allowed to come in contract with oil. The gas is expelled through explosion vent in to atmosphere. The explosion vent’s mouth is covered with aluminum.

……………………….……………….Thank You Sir……………………………………………………..
