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Single Phase SystemInstantaneous PowerThe instantaneous power in an AC circuit is defined as the product of instantaneous voltage (v) across the element and instantaneous current (i) through the element and is denoted by lower case letter p.Instantaneous Power, $\mathrm{p=v\times\:i}$Since, the values of instantaneous voltage and instantaneous current changes from instant to instant, thus the instantaneous power changes with time. The instantaneous power (p) is measured in watts. The instantaneous power may be positive or negative. A positive instantaneous power means power flows from source to load whereas negative instantaneous power means power flows from load to source.Instantaneous Power FormulaCase 1 – ... Read More
The magnetic flux density is the measure of amount of magnetic flux in each square meter of the magnetic field. Therefore, the magnetic flux density is defined as the magnetic flux passing normally (at 90°) per unit area and is denoted by B, i.e., Magnetic flux density, $$B=\frac{\phi}{A}$$Where, Φ is the magnetic flux, A is area normal (or perpendicular) to flux.The magnetic flux density is a vector quantity i.e. it possesses both magnitude and direction.Unit of Magnetic Flux DensityAs we know, the magnetic flux density is$$B=\frac{\phi}{A}=\frac{Weber}{meter^{2}}=Wb/m^{2}=Tesla(T)$$Therefore, the magnetic flux density is measured 𝑊𝑏/𝑚2 or Tesla (T), named in honour of Nikola ... Read More
Capacitance - DefinitionThe ability of a capacitor to store charge is known as its capacitance. In other word, the capacitance can also be defined as the property of a material by virtue of it opposes the any change in voltage applied across it.Capacitance: FormulaExperimentally, it has been found that, the charge Q stored in a capacitor is directly proportional to the voltage across it, i.e.$$Q\propto\:V$$$$Q=CV$$Where, C is a constant and is called as capacitance of the capacitor.$$\Rightarrow\:C=\frac{Q}{V}$$Thus, the capacitance (C) of a capacitor can also be defined as the ratio of the charge on the either plate to the voltage ... Read More
Electromechanical RelayAn electromechanical relay is a type of relay which function using a magnetic field produced by an electromagnetic coil when a control signal is applied to it. It is called as electromechanical since it has moving contacts in the output circuit which are operated by applying an electrical signal.Electromechanical Relay: Working PrincipleAn electromechanical relay transfers signals between its contacts through a mechanical movement. It has three sections viz. input section, control section and output section.The input section consists of input terminals where a small control signal is to be applied. The control section has an electromagnetic coil which gets energised ... Read More
ProblemDraw of ER model for company considering the following constraints −In a company, an employee works on many projects which are controlled by one department.One employee supervises many employees.An employee has one or more dependents.One employee manages one department.SolutionFollow the steps given below to draw an ER model for the company −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows:EmployeeDepartmentProjectDependentStep 2 − Identify the attributes for the given entitiesEmployee − The relevant attributes are name, ssn, sex, address, salary.Department − The relevant ... Read More
ProblemDraw an ER model for library management application considering the following constraints −In a library multiple students can enroll.Students can become a member by paying an appropriate fee.The books in the library are identified by a unique ID.Students can borrow multiple books from subscribed libraries.SolutionFollow the steps given below to draw an ER model for the library management application −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows −BookPublisherMemberSectionGranterStep 2 − Identify the attributes for the given entitiesBook − The relevant attributes ... Read More
ProblemDraw an ER model of the Banking database application considering the following constraints −A bank has many entities.Each customer has multiple accounts.Multiple customers belong to a single branch.Single customer can borrow multiple loans.A branch has multiple employees.SolutionFollow the steps given below to draw an ER model of the Banking database application −Step 1 − Identify the entity setsThe entity set has multiple instances in a given business scenario.As per the given constraints the entity sets are as follows −CustomerAccountAccountLoanLoanStep 2 − Identify the attributes for the given entitiesCustomer − the relevant attributes are customerName, CustomerID, address.Account − The relevant attributes ... Read More
It is the relationship between the instances of two different entity types. Two entities will participate in the relationship.ExamplePerson and events are two different entity types which are related by using the relationship called “attends”.Mapping ER diagram with binary relationshipMapping one to many relationshipExampleHere, Create two tables for two entities.Primary key of one side relation is a foreign key for many side relations.One side relation is customer and many side relations is Order.The primary key cutomerID of the customer is a foreign key of order.The equivalent relations for the above ER diagram are as follows −One-one, many-one, many-many can be ... Read More
The attributes that cannot be divided into sub-parts are called simple attributes. The attributes which can be divided into sub-parts are called composite attributes.ExampleBalance, account number are simple attributesName, address is called composite attributesLet’s consider an example of how to convert Entity Relationship (ER) model of composite attribute to Relational model.Methods for mappingName of relation = Entity set of ER diagramName of column = Attribute of ER diagramExampleIn this example, Name of the relation =studentName of columns=StdID, name, BranchThe equivalent relation for the above ER diagram is −StudentStdIDNameBranchNow apply this technique for Mapping ER diagram with a composite attribute as ... Read More
Key is a data item which is used to identify a record or a value used to identify a record in a database is called a key. It helps uniquely to identify an entity from an entity set.Key allows us to identify a set of attributes that make them sufficient to distinguish entities from each other.ExampleAccount number, employee number, customer number are used as a key field because they specifically identify a record stored in a database.Foreign KeyIn a relation, the column whose data values correspond to the values of a key column in another relation is called a foreign ... Read More