ELECTRICAL COMPONENTS-Ammeter, Voltmeter,galvanometer,multimeter

                                  GALVANOMETER

MOVING COIL GALVANOMETER(MCG)

It is a device used to detect or measure very small amount of current
It works in the principle that when current flows through a rectangular coil kept in a magnetic field,it is deflected.The angle of reflection is proportional to  the current flows through the coil.(when current flows through a conductor a magnetic field is produced around that wire. If the current carrying conductor is placed in a magnetic field due to the mutual interaction between the two magnetic fields, the conductor is deflected)
There are two types of MCG

                         Suspended type

  
     A galvanometer consist of a rectangular coil of large number of turns of insulated copper wire wound on a thin metallic frame.The coil is suspended in between the two horse shoe magnet which can produce a radial magnetic field.The suspension wire used is fine phosphor bronze fibre.A small mirror is also attached to the suspension wire. The lower end of the suspension wire also fixed using phosphor bronze spring.When current flows through the wire the wire gets twisted.

Current sensitivity

The deflection produced in a galvanometer for unit current.

Voltage sensitivity

Deflection produced on a galvanometer for unit voltage.

Figure of merit

The current required to produce a deflection of 1mm on a scale placed at a distance of 1m from the mirror of the galvanometer.

                                        pivoted type

  

 In the pointer type galvanometer, the coil is pivoted on ball bearings.A light aluminium pointer attached to the coil shows a deflection when current is passed. Alight spring attached to the end of the coil provide the restoring couple.

                                     AMMETER
 It uses magnetic deflection. A current carrying coil placed in a permanent magnetic field under go deflection. A spiral spring attached should provide restoring force.An ideal ammeter has zero resistance.

CONVERSION OF GALVANOMETER IN TO AMMETER

A galvanometer can be converted in to an ammeter by connecting a low resistance called shunt resistance parallel to the galvanometer. To measure current ammeter is connected in series with the circuit.

 
                                   VOLTMETER
Voltmeter is used to measure potential difference. A moving coil voltmeter is constructed by connecting a series resistance with moving coil galvanometer.

CONVERSION OF GALVANOMETER IN TO VOLTMETER
A galvanometer can be converted in to voltmeter by connecting a high resistance in series with it.

A Voltmeter is connected in parallel with the circuit element  across which the potential difference is measured. A ideal voltmeter has infinite resistance.




 digital MULTIMETER

It is a digital meter used as voltmeter,Ammeter, resistor checking. It used to measure voltage,current,and reistance.It is a combination of multi range ac voltmeter, multi range dc voltmeter and multirange ohm meter.

 

CELL/ BATTERY

Cell is used to provide potential difference at the ends of a wire.One end of a cell is higher energy it is called positive end.Other end is lower energy called negative.When connected a wire electrical energy is flow from higher energy to lower energy

                  DRY CELL
It consist of a metallic jar of zinc,it serves as the negative electrode.. The carbon rod through the center is the positive electrode.The electrolyte is in the form of paste of ammonium chloride and zinc chloride.It is mixed with powdered coke and graphite and manganese dioxide.The manganese dioxide prevent the formation of gaseous hydrogen. When cell is connected in a circuit zinc atom loses two electrons per atom.The electrons flows in the circuit and pass in to solution.The ammonium ions in the electrolyte remove electrons from the carbon anode
           VOLTAIC CELL

                                 Constuction of a simple voltaic cell

It is an electrochemical cell. It convert chemical energy to electrical energy

It consist of a glass vessel containing dilute Sulphuric acid . Zinc and copper Plates are placed in the acid (from the bottom side of the battery you will get zinc, a piece of earth wire used in household wiring can be used as copper)

The rods are connected to a LED bulb through a copper wire.The bulb lights up

Electrons flows from Zinc to Copper.The conventional current flows from Cu to Zn

RESISTANCE BOX

It is used to provide an obstruction (hindrance) to current flow as the resistance increases current flow decreases

BULB

It convert electrical energy to light energy. Different types of bulbs are available. The power of the bulb is  represented as Watt. If the wattage is less less electrical energy is needed. Incandescent lamp utilize the Heating effect of current. Compact Fluorescent lamps are low Wattage. The most efficient and very low wattage bulbs are LED lamps

              
INCANDESCENT LAMP

It is also known as filament lamp.A Tungsten filament is placed inside a glass bulb.wires supports the filament .Electricity flows throw this wires and filament

Why Tungsten is used as filament?

It has very high melting point(3410 c),high resistivity,high ductility(we can make it very thin wire), when heated light is emitted

Why inert gas is filled in this glass bulb?

At high temperature there is a chance of evaporation of Tungsten. To reduce evaporation inert gas filled inside the glass bulb. It increases the life of the bulb

In early days vacuum bulbs are used what is its disadvantages?

Tungsten filament gets evaporated faster.glass changes to black in color, the life period is very less

What is the energy change take place in the bulb?

electrical energy changes to heat and light

Who discovered filament lamb?

Thomas Alva Edison

 What is the average life period of an incandescent lamp?

1000 hours

Why the filament of  some bulb melts rapidly?

Some manufacturing defects such as not filling the inert gas inside the glass bulb properly. The heating expansion of glass and filament and filament connecting wires are slightly different. because of this inert gas may escape from the glass bulb. The over current flow in the circuit may also melts the filament

Is Zero watt filament lamp is possible?
No, if the power is zero no light is emitted, they have 5w incandescent lamps

  DISCHARGE LAMPS

Main parts  of a discharge lamp is

A glass tube filled with suitable gas at low pressure, Electrodes at both ends of the tube,heating coil at the ends of both electrodes

 A high voltage is applied on the electrodes of the tube. The gas gets ionized.Electrons emitted from the heating coil collide with the atoms present in the glass tube.The electrons in the atom get energy and excited to higher energy states.When the excited electrons gets back to the normal energy state infrared, ultra violet,visible rays are emitted

As the result of collision of electrons and ionized atoms with unionized atoms emits light. Color of light depends on the nature of gas taken in the tube

GAS in the tube                      Color of light emitted

 Neon                                                Orange RED

Nitrogen                                            Red

Sodium vapour                                  Yellow

Mercury vapour                                White

Chlorine                                             Green

Hydrogen                                           Blue

Mercury vapour lamp

Sodium vapour lamp

Xenon Arch discharge lamp

Fluorescent lamp

It is the most Commonly used disharge lamp.When electricity flows through the heating coil it gets heated and electrons are emitted.To increase the electron emitting heating coil is coated with thorium oxide.The mercury in the tube gets evaporated. The electrons emitted from the heating coil  collide with mercury atom as a result of this ultra violet rays are emitted.These rays are absorbed by the fluorescent material coated inside the tube and changes it in to visible light

Compact fluorescent lamp(CFL) 
CFL gas a unit of electronic circuit and a fluorescent tube containing mercuric vapour. With the help of electronic circuit high frequency electricity is (50KHz) is supplied between the electrodes of the tube.As a result electrons are emitted from electrodes. These electrons collide with mercury atoms ultraviolet radiation emitted. Fluorescent coating with in the tube convert  UV rays to visible light

Advantages of discharge lamp over incandescent lamp

A very low power is enough
The life period is 5 times that of a incandescent lamp
Gives more intense light
Majority of electricity convert to light
Disturbance due to shadow is very less

   RHEOSTAT
It is used to vary the resistance. Varying the length of wire we can change the resistance. length of wire is directly proportional to resistance