Topics in Basic TechnologyCeramics: Types of Ceramics Advantages and Disadvantages of Chain drives Len Academy Questions for Basic Technology JSS3, 2nd Term, 2020 Len Academy Question for Basic Technology, JSS3, 2nd Term, 2020, Part 2 Belt and Pulley Drives: Types of Belt in Belt Drives Electromechanical Energy: Parts of the Refrigerator and how they operate Chain Drive, Types, Classifications, Advantages and Disadvantages Advantages and Disadvantages of Belt Drives Type of Lines in Technical Drawings Len Academy questions for Basic Technology, JSS2, 2nd Term Len Academy questions for Basic Technology JSS2, 2nd Term, Part 2 Maintenance, Types of Maintenance Hardwood and Softwood - Characteristics and Examples What are Ceramics? Characteristics of Ceramics
Academic Questions in Basic Technology
The following statements are true concerning wood except _____.
A. It is an inorganic material
B. It is a structural tissue
C. It is composed mainly of cellulose
D. Hardwood and Softwood are types of wood
E. It constitutes the stems and branches of trees
F. It is porous and fibrous
Which of the following is not a characteristic of hardwood?
A. They are more fire resistant in comparison to softwood
B. Their stem are divided into trunks called dendritic form
C. Birch, Teak and Alder are examples of hardwood
D. They always have a higher density than softwood of the same mass
E. They are suitable for making deckings in buildings
F. Most hardwood are expensive than softwood
The outermost covering of a wood is called the _____.
A. Wood skin
The followings are characteristics of ceramics except _____.
A. They readily undergo oxidation
B. They have high melting point
C. They are durable
D. Most are insulators but graphite is a conductor of electricity
E. Most are non-magnetic
F. They have great tensile strength but graphite is soft
Which of the following statement is false of ceramics?
A. They are not metals
B. They are not plastics
C. Ceramics can be absolutely defined by its products characteristics
D. Ceramic materials are not organic in nature
E. Ceramics are refractory in nature
F. Ceramics materials are usually made from clay
Which of the following is not a function of thin continuous line in Technical drawing?
The following are Types of Line in Technical Drawing EXCEPT _____.
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Electromechanical energy consists of two forms of energy. These are:
Electromechanical energy can simply be put as a conversion of electrical energy to mechanical energy or (mechanical energy to electrical energy); as seen in various appliances; for instance, the refrigerator.
Devices that make use of electromechanical energy are called electromechanical devices. They include the refrigerator, air conditioner, loudspeakers, microphones and so on.
In this article, we will explore on the refrigerator and it’s mechanism of operation.
The refrigerator comprises of both the fridges and deep freezers whose functions serve the storage of edible material and other substances. They also function to keep food substances cold for the satisfaction of people and for commercial purposes.
Medical and Chemical industries use the refrigerator to preserve drugs and other important chemicals at a temperature in which the various decomposition micro-organisms are unable to act.
Below are some of the major parts or components that make up a refrigerator:
The diagram below shows the major components of a Refrigerator:
The refrigerant can be a liquid (fluid) or gas (vapor), and it runs throughout the various tubes or compartments of the refrigerator.
The refrigerant (fluid in this instance) flows throughout the entire pipes of the refrigerator. This fluid refrigerant would expand from its liquid state into a vapor state (becomes vapor refrigerant because it takes in heat from its surroundings), thus bringing about the cooling process inside the fridge or freezer.
The refrigerant (fluid) absorbs heat from the substances to be cooled (present in the evaporator). As a result, the fluid refrigerant becomes vapor.
Conversely, the condenser condenses the refrigerant (vapor) into liquid (fluid refrigerant). This process will be explained in a latter part of this article.
Both aformentioned processes repeats itself in cyclical manner; and is referred to as the refrigeration cycle.
The evaporator is the cooling chamber where food materials are kept in the refrigerator. It acts by extracting heat from the food items in order to bring about their coldness.
The evaporator is a heat exchanger and it's made up of several turns of coil (made of aluminium or copper). The evaporator simply refers to the coil in the refrigerator where cooling and freezing is achieved.
It is within the evaporator that the refrigerant absorbs the heat from the substance to be cooled.
Note: The evaporator is also called the freezer or the chiller.
The compressor of a refrigerator is always seen at the back and bottom portion of the refrigerator. It is the mechanical section of the refrigerator in which the refrigerant is compressed into a vapor state.
The compressor acts by sucking the gaseous or vapor refrigerant from the evaporator; as it releases it at a high temperature and pressure.
The sucking/pumping action of the compressor occurs from the low pressure evaporator to the high pressure condenser.
The circulation of the refrigerant in the refrigeration system is brought about through the pumping action of the compressor.
Note: The compressor is driven by an electric motor which makes it the major power consuming part of the refrigerator.
The condenser comprises of a series of arranged pipes or (coils of copper tubing) at the lower posterior end of the refrigerator, from where heat is lost to the atmosphere.
The compressor pumps the refrigerant into the condenser where it is cooled by atmospheric air. The condenser thus absorbs heat through the aforementioned process.
Note: Since heat is extracted by the condenser, it becomes very hot as a result.
The condensation of the gaseous refrigerant occurs in the condenser. This simpy means that the refrigerant changes its state from vapor to liquid (fluid) within the condenser.
In short, the condenser condenses the gaseous refrigerant (changes its state to from gas to liquid).
The refrigerant that leaves the compressor is now a liquid. As the liquid (fluid) refrigerant flows, it becomes expanded on its path to the evaporator. This expansion process causes the liquid refrigerant to evaporate into its gaseous state (in the evaporator).
As soon as the gaseous refrigerant enters the capillary or expansion valve, its temperature and pressure drops, as it cools again. This cooling refrigerant cools the evaporator as it flows through the pipes in the evaporator.
The expansion valve is also called the capillary.
This is the temperature controlling device on the refrigerator. Recall that temperature is the degree of hotness or coldness of a body.
The thermostat consists of a sensor connected to the evaporator. The (settings) on the button of the thermostat can be adjusted in the compartment of the refrigerator where it is located.
If the set temperature (on the thermostat) is reached within the refrigerator, the thermostat shuts down the power supply to the compressor. This results in a reduction of temperature in the refrigerator. To this end, you may have observed a stoppage in the function of the refrigerator (similar to muting/stopping a sound); and after some time, the refrigerator resumes its activity (similar to starting its sound).
As the name implies, the defrost system of the refrigerator functions to remove excess ice from the surface of the evaporator.
Note: The thermostat button can also be used to achieve this function when it is pressed.
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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.
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NOTABLE POINTS IN Basic Technology
Ceramics are refractory. They also require a very high amount of heat and subsquent cooling to be formed.
Being refractory means that they are capable of withstanding a variety of abuses like high temperatures and chemical attacks.
Ceramics are generally made by taking clay from the ground and mixing it with water. It is then shaped into any form and fired inside an oven (called kiln) at a very high temperature. They may then be decorated with a waterproof, paint-like substances called glazes.
Ceramics may have constrasting physical and chemical properties (or characteristics); but in general,
They have high melting points.
They are heat resistant.
They can be very hard with great strength; although a few are brittle or soft; for example, graphite.
They are durable (last for a long time).
Most are electrical insulators (cannot conduct electricity) but; graphite is an electrical conductor.
They are chemically unreactive or inert.
They are not easily oxidized.
Most are non-magnetic.