Physics notes class 7 electricity

      PHYSICS NOTES
      
           Electricity

           Important points

*Electricity-The flow of charges or electrons is called electric current. Such phenomena is called electricity. 
*It is of two types :
( 1) Static electricity = The electricity which is generated by rubbing is called Static electricity. 
* Current electricity : The electricity in which there is continuous flow of charges is called current electricity. 

* Voltage : it is also known as potential difference. The work is done to carry one unit of positive charge from one point to another point in an electrical field. 
NOTE :It is measured in unit volt . 

*Electric circuit : The closed conducting path along which electric current flows is called electric circuit. 

* IT HAS 4 COMPONENTS:
(1) A source of electric current
Example : cell or battery  
(2) A conducting wire 
(3) A switch or a key 
(4)  Load 
Example: electric appliances  

*Circuit diagram : When all the components of electric circuit is represented by a symbol in circuit  then it is called Circuit Diagram.
 
*Battery : The combination or grouping of cells is called battery. 

*IT IS MAINLY OF 2 TYPES :
(1) Series Combination : A combination in which the negative terminal of one cell is connected to positive terminal of another cell and so on is called series combination.
 
(2)  Parallel Combination: The combination in which negative terminal of all the cell are connected together and positive terminals of all the cells are also connected together. 
 

*Storage cells : Rechargeable batteries are called Storage cells. 

*Resistance: The property of material by virtue of which it opposes the flow of electric current is called resistance. 

* THE RESISTANCE DEPENDS ON :
(1) Length of the wire 
(2) Area of the cross section of the wire  
(3) Temperature
(4) Material of the wire

NOTE .. 
(1) Electric current is inversly proportional 
to the resistance I. e. If resistance of the wire will increase then current flowing in the wire would decrease  and vice - versa . 

   *  HEATING EFFECT OF ELECTRIC CURRENT : when an electric current is passed through a high resistance wire and heat is produced then this effect of electric current is called Heating effect of electric current. 

THE AMOUNT OF HEAT PRODUCED DEPENDS ON :
(1) RESISTANCE OF THE WIRE 
(2) MAGNITUDE OF ELECTRIC CURRENT PASSED THROUGH THE WIRE 
(3) NATURE OF THE MATERIAL OF THE WIRE. 

DISADVANTAGE OF HEATING EFFECT OF CURRENT: When electric current passes through the wire  it's some part of electrical energy is converted into heat energy . So this is wastage of energy. 
The produced heat damages the electrical components and sometimes causes fire. 

*Short Circuit: A sudden flow of large amount of current due to direct contact of live and neutral wire  
When live and neutral wire comes to the contact of each other, then their resistance becomes 0 and hence a large amount of current starts to flow through the wire. 

* Overloading: when a number of devices are connected to a single socket, then they draw extremely large current from the circuit, this condition is called overloading. 

* Safety fuse : A safety fuse is a device made up of lead and tin and works on the heating effect of the electric current. 
It has a wire which has a low melting point  When the electric current becomes excessive due to short circuit or overloading, it melts and breaks the circuit immediately and hence helps in the protection of various electrical appliances. 

   * Electric bulb : It is a device that converts electrical energy into light energy . It works on the heating effect of the electric current. 
It contains a thin glass covering on the outer side. It has a long  thin and curly tungsten filament. It is filled with inert gas , Argon . When electric current passes through the filament and gets heated because it is a high resistance wire and therefore it starts to glow . Due to it's high melting point  it doesn't melt. 

*MAGNETIC EFFECT OF ELECTRIC CURRENT:
When electric current passes through a wire then current carrying wire produces magnetic field around it. This effect of electric current is called Magnetic effect of electric current. 

*Solenoid : long  ,cylindrical and helical coil of insulated wire whose length is more than it's diameter . 

* Electromagnet : A magnet produced by passing an electric current through a coil of insulated wire wound around a soft iron rod is called Electromagnet . 

THE STRENGTH OF ELECTROMAGNET DEPENDS UPON: 
(1) THE no. of turns of insulated wire  
(2) The magnitude of electric current passing through it . 

* Electric bell : The electric bell works on the magnetic effect of electric current. It is a device that converts electrical energy into mechanical energy to produce sound. 

CONSTRUCTION : The electric bell has U - shaped electromagnet . In the front of it , armature is placed. The lower end of armature is attached to a flat spring and it's upper end is attached with a hammer  Near the hammer, there is a metallic gong which is connected with contact screw that touches the armature and electromagnet is attached with cell  ,wire and switch to complete circuit. 

Working: when we press the switch then the circuit completes and electromagnet attracts the armature towards it and hence hammer strikes the gong and sound is produced. When the armature moves towards the magnet , then the circuit breaks and electromagnet looses it's magnetism and hence the spring brings back the armature . Then the circuit completes again and this continuous process  produces sound. 




Comments

  1. Unknown30 June 2020 at 05:38

    It is really helpful for me.
    Being in class 7,i have got too much knowledge in this chapter that is electricity

    ReplyDelete

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