Fundamentals of Electromagnetism

 Objective: Students should be able to explain the basic concept of electromagnet

Orested Law ;  Orested states that "steady current creates magnetic field".

                                       

                                                                     Fig.1 Orested Experiment

There is a conductor , a battery and a compass shown in figure.  Comoass is place near the current carrying conducter. When battery is connected current will start to flow. So as shown in first condition compass will deflect from middle position which show present of external magnetic field. 

Now connection of battrery is altered so direction of deflection is also change shows that direction of magnetic field will change by changing the direction of current. In the third figure imaginary magnetic field line are shown. which can be easily understand by Right hand thumb rule.

Right hand thumb rule: According to this put your right hand  thumb in direction of current and  rotate the finger than rotation of finger will show the direction of magnetic field.

       

Fig 2  Right Hand Thumb Rule

For finding magnetic field in loop we can apply right hand thumb rule as loop is made of a infifnite lines  (As theory of integration states that every curve is made of infine streight line)  and got direction of magnetic field as shown in fiure.

Fig 3 magnetic field in a loop

We can find out direction of magnetic field in a loop easily. If we rotate fingers of right hand thumb in direction of current than thumb will show the direction of magnetic flux inside the conductor.

 Electromagnet : If we make winding on a soft iron piece and connect this winding to battrey than current will flow and it will create a magnetic field and iron piece will magnetised. this will attract or repel other magnet. this magnetism is due to electrical supply and present untill battery is connected so it is called Elecromagnet. this electromagnet having two imaginary pole,north pole(N) and south pole(S)

fig4

If direction of current is reverse than direction of magnetic fiel is also reversed means N pole and S pole will interchanged.

fig5  electromegnet

Extra Edge: Magnetic field rotates around current carrying conductor. If loop is form than magnetic field becomes inside or outside the loop. winding is made of so many loops. so that this magnetic field becomes more strong. if iron pieces are place inside the winding than  magnetic field becomes more stronger due to high permeability of iron.

                                        

                                                              fig6     working of electromagnet   

Application: 

1. Simple electromagnetic relays

2.Transformer

3 Rotating machines

                                         Assignment - 

Q1 what will happen if voltage of battery is increased?

Q2 what will happen if low frequency ac source is connected by removing battery?

Q3 If winding pattern is change then poles wilol remain same or change and why

Refrences:- fig 1 wikipedia 

                    fig 2 electrical 4 u

                    fig3-6 from google images