ARTICLE OF PHYSICS

                                                                 ELECTRIC POWER

When an electric current flows through a conductor , electrical energy is used up and we say that the current is doing work. we know that the rate of doing work is called Power, so electric  power is the electrical work done per unit time.

 

                                                        POWER = WORK DONE/ TIME TAKEN                 

                                                        OR p = w/t

 

 UNIT OF POWER :-

   The SI unit of power is WATT and CGS unit is JOULES

                                         1 watt = 1 j/1sec

 

                                             Joule’s Law Vs. Ohm’s Law

A historical note: it was James Prescott Joule, not Georg Simon Ohm, who first discovered the mathematical relationship between power dissipation and current through a resistance. This discovery, published in 1841, followed the form of the last equation (P = I2R), and is properly known as Joule’s Law. However, these power equations are so commonly associated with the Ohm’s Law equations relating voltage, current, and resistance (E=IR ; I=E/R ; and R=E/I) that they are frequently credited to Ohm.

 

joules vs ohms power equations

 

Power measured in watts, symbolized by the letter “W”.

Joule’s Law: P = I2R ; P = IE ; P = E2/R

 

 

                                                 RESISTANCE AND RESISTIVITY

RESISTANCE :-  The property of material to oppose the flow charge

> The material which have resistance called Resistor

> SI unit is Ohm's

 

FACTOR AFFECTING  RESISTANCE

1. The length L of the material. Longer material have greater resistance

2. The cross-sectional area A of the material. Larger area offer LESS resistance

3. The temperature T of the material. The higher temperature usually result in higher resistance                 

4. The kind of material. Iron has more electrical resistance than a geometrically similar copper conductor

 

RESISTIVITY :- A measure of the resisting power of a specified material to the flow of an electric current

> The  SI unit is Ohms meter and CGS unit is Ohms centimeter                                       

 

FACTOR AFFECTING  RESISTANCE

1. Temperature

2. Alloying

3. Mechanical stressing         

 

                                                       ELECTRIC  CURRENT

> It is the rate of flow of charge with respect to time through particular cross-sectional area of conductor.

 

SI UNIT :- Ampere (A)

CGS UNIT :- Biot

 1biot = 1

   Current = Charge/time

An electric current is the rate of flow of electric charge past a point or region. An electric current is said to exist when there is a net flow of electric charge through a region. Electric charge is carried by charged particles, so an electric current is a flow of charged particles. The moving particles are called charge carriers, and in different conductors may be different types of particle. In electric circuits the charge carriers are often electrons moving through a wire. In an electrolyte the charge carriers are ions, and in an ionized gas (plasma) are ions and electrons.

 

                                                 ORESTED'S EXPERIMENT

1. The magnetic effect of current was discovered by H.C. Oersted in 1820. He observed that flow of electric current through a conductor produce a magnetic field around it. The magnetic effect of current can be demonstrated by doing following experiment.

 

Experiment to Demonstrate the Magnetic Effect of Cu

 

  First of all make a simple electrical circuit by joining a long straight wire with a battery and a plug. Now, take a magnetic compass needle and place the straight wire parallel to and over the compass needle. Then switch on the circuit so that current flows through the wire from south to north directions. Now, you will found that the north pole of compass needle gets deflected

towards the west.

 

But, if the direction of current in the wire is reversed then the north pole of the compass needle gets deflected towards the east. The direction of deflection of magnetic needle can be easily determined by SNOW rule. According to SNOW rule, when current flows through a conductor from South to North direction and the wire is held over magnetic needle then the north pole of the magnetic needle deflects towards west.

                               

                                  AMPERES SIMMIMG RULE

Ampere's swimming rule states that, "If a man swims along the wire carrying current such that his face is always towards the magnetic needle with current entering his feet and leaving his head, then the north pole of the magnetic needle is always deflected towards his left hand."

 

                                         FLEMINFG LEFT HAND AND RIGHT HAND RULE

>Whenever a current carrying conductor comes under a magnetic field, there will be a force acting on the conductor. The direction of this force can be found using Fleming’s Left Hand Rule also known as ‘Flemings left-hand rule for motors’

 

>Similarly if a conductor is forcefully brought under a magnetic field, there will be an induced current in that conductor.

  The direction of this force can be found using Fleming’s Right Hand Rule.

 

>In both Fleming’s left and right hand rules, there is a relation between the magnetic field, the current and force.

 This relation is directionally determined by Fleming’s Left Hand rule and Fleming’s Right Hand rule respectively.

 

>These rules do not determine the magnitude but instead show the direction of any of the three parameters (magnetic field, current, force) when the direction of the other two parameters is known. 

 

Fleming’s Left-Hand rule is mainly applicable to electric motors and

Fleming’s Right-Hand rule is mainly applicable to electric generators.

 

                                                KICKING WIRE EXPERIMENT

 

    Take a flexible copper wire AB and suspend it from a rigid support with the help of a flexible joint Place a U shaped magnet around the lower end B of the wire. In the center of the U shaped magnet place a vessel filled with mercury in such a manner that the lower end B of copper wire touches the surface of mercury. Now, connect the upper end A of wire with the positive terminal of battery and dip another wire from the negative terminal of the battery in the vessel filled with mercury. In this way the circuit gets completed. Now, insert the key. When the key is inserted, the current flows through the wire from end A to B perpendicular to the magnetic field and the wire is kicked outward. This happens because when current passes through a wire placed in a magnetic field, it experiences a force which jerks it in outward direction. It should be noted that the direction of force acting on a current carrying wire placed in a magnetic field is always perpendicular to both the direction of current and magnetic field. 

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                                                                  ELECRIC GENERATOR

1. It is an electrical machine which convert mechanical energy into electrical energy.

 

*Principal of electric energy

  It is based on electromagnetic induction when force is applied perpendicular to magnetic           field current perpendicular to both induced in the armature coil and direction can be found by using fleming right hand rule  

 

CONSTRUCTION:-

 Armature having several coil of conducting wire which are insulated with each other placed in between concave faced magnetic poles. This armature is further connect with slipring in case of AC generator and with split slipring  in case of DC generator , These slip are further connected with graphite brush and Graphite brush is further connected with AC and DC circuit the shaft armature  powered by using any engine.

 

 

WORKING OF ELECTRIC GENERATOR:-

1. When force on AB  part of armature is upward and magnetic fields line is form North to   South , then current induced parallel to both magnetic field and current induced  from  A to B part in AB part armature.
2. When force on CD  part of armature is downward and magnetic fields line  is form North to   South , then current induced parallel to both magnetic field and current induced  from  C to D part in CD part armature

 

 

    ELECTRIC FUSE

 

 

 

In electronics and electrical engineers, a fuse is an electrical safety device that operates to provide overcurrent  protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It is a sacrificial devices  once a fuse has operated it is an open circuit, it must be replaced or rewired, depending on type. Fuses have been used as essential safety devices from the early days of electrical engineering. Today there are thousands of different fuse designs which have specific current and voltage ratings, breaking capacity and response times, depending on the application. The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Wiring regulations usually define a maximum fuse current rating for particular circuits. Short circuit , overloading, mismatched loads, or device failure are the prime or some of the reasons for fuse operation. A fuse is an automatic means of removing power from a faulty system; often abbreviated to ADS (Automatic Disconnection of Supply. Circuit breakers can be used as an alternative to fuses, but have significantly different characteristics.