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1)       What are the advantages and disadvantages of ac, dc motors?

Advantages of AC Motors:

·         Low cost,

·         long life,

·         high efficiency,

·         large ratings available (to 1 MW or more),

·         large number of standardized types.

Disadvantages of AC Motors:

·         Starting inrush current can be high,

·         Speed control requires variable frequency source.

Advantages of DC Motors:

·         Precision positioning,

·         High holding torque,

·         Long lifespan,

·         Low maintenance,

·         High efficiency

Disadvantages of DC Motors:

·         Some can be costly,

·         Require a controller,

·         Higher initial cost,

·         Requires a controller.

2)       How the efficiency of motor is is calculated?

To calculate a motor’s efficiency,

the mechanical output power is divided by the electrical input power: 

,

where  is energy conversion efficiency ,  is electrical input power, and  is mechanical output power.

In simplest case , and , where V is input voltage, I is input current, T is output torque, and  is output angular velocity. It is possible to derive analytically the point of maximum efficiency. It is typically at less than 1/2 the stall torque.

3)       What are the standards of motor?

The following are major designs and manufacturing standards covering electric motors:

·         International Electro-technical Commission: IEC 60034 Rotating Electrical Machines

·         National Electrical Manufacturers Association (USA): NEMA MG 1 Motors and Generators

·         Underwriters Laboratories (USA): UL 1004 – Standard for Electric Motors

4)       Define an Electromagnet?

An electromagnet is an object that acts like a magnet, but its magnetic force is created and controlled by electricity–thus the name electromagnet. By wrapping insulated wire around a piece of iron and then running electrical current through the wire, the iron becomes magnetized. This happens because a magnetic field is created around a wire when it has electrical current running through it. Creating a coil of wire concentrates the field. Wrapping the wire around an iron core greatly increases the strength of the magnetic field.

5)       What do you mean by right hand rule?

To find the direction the magnetic field is going, you can use the “right-hand rule” to determine it. If you take your right hand and wrap it around the wire, with your thumb pointing in the direction of the electrical current (positive to negative), then your fingers are pointing in the direction of the magnetic field around the wire.

6)       Give some strength of electromagnetic fields.

Following are the some of the major strengths of electromagnetic fields-
Unit

The unit of magnetic force is called the tesla (T). Near a strong magnet the force is 1-T. Another unit used is the gauss, where 104 gauss (10,000) equals 1 tesla.

Current

The strength of the magnetic field is proportional to the current in the wire. If you double the current, the magnetic force is doubled.

Since Voltage = Current x Resistance (V = I*R), you can double the current in a wire by doubling the voltage of the source of electricity.

Turns of coil

If we wrap the wire into a coil, you increase the magnetic force inside the coil, proportional to the number of turns. In other words, a coil consisting of 10 loops has 10 times the magnetic force as a single wire with the same current flowing through it. Likewise, a coil of 20 loops has 2 times the magnetic force than one with 10 loops.

Varies with distance

The magnetic force decreases with distance. It varies inversely proportional to the square of the distance. For example the force at 2 cm. from a wire is 1/4 that of at 1 cm. and the force at 3 cm. is 1/9 the force at 1 cm.

7)       What do you mean by electromagnetic induction?

Electromagnetic induction is a process where a conductor placed in a changing magnetic field causes the production of a voltage across the conductor. This process of electromagnetic induction, in turn, causes an electrical current – it is said to induce the current.

8)       What do you mean by magnetic flux?

Magnetic flux is the magnetic lines of force produced by a magnet. It is measured by the unit Weber. A Weber (Wb) is equal to 100,000,000 maxwell(s). Flux density (B), a measure of the strength of a wave, is equal to the number of magnetic lines of flux per square meter in terms of the unit Tesla (T), where B = Wb/A.

9)       What is an electromagnetic wave?

Electromagnetic waves are formed when an electric field couples with a magnetic field. The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.

 

10)    State the applications of electromagnetism.

Primary electromagnetic device is the relay. The action of the armature, spring, and coil is the same in all relays. Notice, however, the schematics are only different as far as the contacts are concerned. Relays are usually used to control high-voltage switching (contact use) with a low-voltage control application (the coil winding). They may also be used as remote control devices. Relay contacts are normally open (until armature action closes them) or normally closed (until armature action opens them). Contacts have pole configurations similar to switches.

11)    What do you mean by argument passing mechanism in C language?

The exact mechanism for assigning arguments to parameters, called argument passing, depends upon the evaluation strategy used for that parameter (typically call-by-value), which may be specified using keywords. When we pass a value either by value or by reference in Visual Basic, then it is known as the Passing Parameter. The Passing Mechanism is related to different programming languages like C and Visual basic. There are different ways of passing argument which are stated as follows:

12)    What is an Argument in c programming?

Arguments are more properly thought of as the actual values or references assigned to the parameter variables when the subroutine is called at runtime. Arguments are the type of variables that can be used by the functions in C language. An Argument is similar to a parameter and is something that has been passed to a function.

For Example,

int main(int argc, char **argv);

“argc” and “argv” are the arguments which are being passed into the main function.

13)    What do you mean by call by value and call by reference argument passing mechanism?

When passing data by value, the data is copied to a local variable/object in the function. Changes to this data are not reflected in the data of the calling function. For larger objects, passing data by value can be very expensive.
When passing data by reference, a pointer to the data is copied instead. Changes to the data pointed to by the pointer are reflected in the data of the calling function. Regardless of the size of the object, passing data by reference always has the same cost.

14)    What is the difference between users defined function and library function?

User Defined Functions has to be Developed by the user at the time of writing a program like Main() while library defined functions are already defined in the library of C and cannot be further modified like Printf().

15)    What are the advantages of user-defined function?

Following are the advantages of user-defined function:

·         It facilitates top down programming.

·         It can be used by any other program.

·         Length of program can be reduced and makes debugging easier.